I'm willing to bet the serial port driver is the 'SOL' driver for the Intel AMT remote access feature. Yep, i was right this system supports 'AMT' but only up to win 7 and possibly 8. Intel AMT LMSSOL for AMT 5.xx is the serial/program package you would install under win 7 and this package is not compatable under win 10. Go to Device Manager by going tostart / search box and type device manager and enter and then double-click on the program icon that appears. Check each device for a red x, yellow! These identify devices with problems (probably drivers, but also conflicts or something else). Click on each for further details and troubleshooting tips.
The USB-A and USB-B connection types are what most users are accustomed to. However, these days, there are more things you can achieve with the new USB-C type of connection. With this option, users can charge their computer. What’s more, they can also connect their PC to other USB-C type devices, including media players, smartphones, docking stations, and display adapters, among others.
However, we are aware that a good percentage of users are having troubles with their USB-C connection. In most cases, the problems are caused by problems with the hardware or software. Don’t worry because you can easily fix USB-C issues in a Windows 10 computer. After all. You will get notifications which you can use to determine how to resolve the problem.
What is a USB-C connector?
Developed by the USB Implementers Forum, the USB-C connection type is a tool for transmitting both power and data. It is worth noting that this was designed, certified, and released as an industry-standard connector by the members of the organization. Over 700 companies are part of the USB Implementers Forum, including Apple, Microsoft, Dell, HP, Intel, and Samsung. This is also the reason why many computer manufacturers readily accepted USB-C technology.
Is it similar to a micro USB connector?
At first glance, the USB-C connector looks a lot like a micro USB connector. However, the former has a distinct oval shape. Moreover, it is a little bit thicker to accommodate its best feature—like MagSafe and Lightning, the USB-C connector does not have an up or down orientation. You simply have to line the connector correctly, and you wouldn’t have to worry about flipping it to plug it in properly. Another key thing to remember is that the cables have the same connectors on both ends. This means that you would not have a hard time figuring out which end goes where.
Comparing USB-C and USB 3.1
The USB-C connection type’s default protocol is USB 3.1. Theoretically, at 10Gbps, USB 3.1 is twice as fast as USB 3.0. However, the ports for USB 3.1 can still be found in their original, larger shape. Such ports are referred to as ‘USB 3.1 Type-A. Generally, it has become more common to see USB 3.1 ports with USB-C connectors.
How to fix USB-C issues in a Windows 10 computer
Some of the notifications you might encounter when the USB-C connection is not working include the following:
- You might be able to fix your USB device
- Slow USB charger connection
- Display connection might be limited
- PC isn’t charging
- The USB device might not work
- These two devices can’t communicate
- The USB device might not be working properly
- Use a different USB port
- The USB or Thunderbolt device functionality might be limited
Every notification has its solution. Whether you need to fix USB-C compatibility or update your drivers, there’s always something you can do to resolve the issue.
What to do when you see the ‘You might be able to fix your USB device’ error notification
If you see this notification while trying to use a USB-C connection type, there must be something wrong with the device or the drivers on your computer. You can run the troubleshooter for hardware and devices, or you can update your drivers to resolve the problem.
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Running the Hardware and Devices troubleshooter
- On your keyboard, press Windows Key+S.
- Type “control panel” (no quotes), then hit Enter.
- Once Control Panel is up, go to the top-right corner of the window and click the View By option.
- Select Large Icons from the options.
- Click Troubleshooting.
- Go to the left-pane menu, then click View All.
- Select Hardware and Devices.
- Click Next, then follow the on-screen instructions.
The tool will start to identify issues with your hardware and devices, attempting to repair them.
Using Windows Update to fix the device drivers
- Right-click the Windows icon on your taskbar.
- Select Settings from the list.
- Click Updates & Security.
- Go to the left-pane menu and select Windows Update.
- Go to the right pane, then click Check for Updates.
- Install all the available updates.
Updating your device drivers
It is possible that the device drivers in your computer are corrupted, damaged, or outdated. You can update them to give your unit a fresh set of drivers. There are two ways you can do this—going to the manufacturer’s website or automating the update process, using Auslogics Driver Updater.
It is worth noting that manually updating your drivers can be time-consuming and risky. As we’ve mentioned, you have to search for the compatible drivers on the manufacturer’s website. If you download and install the wrong drivers, you might cause more problems to your computer.
Resolve PC Issues with Driver Updater
Unstable PC performance is often caused by outdated or corrupt drivers. Auslogics Driver Updater diagnoses driver issues and lets you update old drivers all at once or one at a time to get your PC running smoother
On the other hand, when you automate the process with the help of Auslogics Driver Updater, you are avoiding possible PC damage. The best part is, the tool will take care of all problematic drivers—not just the one which caused the USB-C connection type problem. So, you will notice a significant improvement in your PC’s performance and speed.
Finding the error codes for device issues
It is important to know the error code to address problems with your device appropriately. To acquire the error code, simply follow the steps below:
- Right-click the Windows icon on your taskbar.
- Select Device Manager from the list.
- Right-click the problematic device, then select Properties.
- Go to the Device Status dialog box to see the error code.
How to fix slow USB charger connected
When the ‘slow USB charger connected’ notification shows up, there are various possible reasons behind it. Here are some of them:
- You’re using a charger that is not compatible with your device or computer.
- Your charger’s power is insufficient for your device or computer. It is worth noting that devices with USB-C connectors have larger power limits. So, charging should be faster with greater levels of power, as long as the device supports USB power delivery.
- You have not properly connected the charger to the port on your device or computer.
- The cable’s power capacity is not sufficient for the charger itself, the device, or the computer.
- Your USB port is dusty or dirty, preventing proper insertion of the charger.
- You’ve connected the charger to your device or computer through an external dock or hub.
You can fix this problem by using the charger and cable that came with your device. These peripherals are designed according to industry standards. So, they have the right power capacity to speed up charging. On the other hand, you can also check if your charger is properly connected to the USB-C port on your device or computer. If the port is dusty or dirty, you can use compressed air to clean it.
Note: Systems with available USB-C connectors have higher power limits, and they can support up to 5V, 3A, or 15W.
Resolving the ‘Display connection might be limited’ error notification
There are many reasons why you see this error notification. It is possible that the dongle has new features that the cable, device, or PC do not support. You should also check if you’ve connected the dongle to the correct port or through an external dock or hub. On the other hand, it is possible that the other devices with the USB-C connection are interfering with the dongle.
You should know that a USB-C connector has Alternate Modes which you can use for non-USB connectors. These modes are HDMI, DisplayPort, and MHL. So, you can resolve the ‘Display connection might be limited’ error notification by checking if your PC, cable, and external display support the aforementioned alternate modes. You can also try to check if the dongle or device is directly connected to your computer. If it is yet the problem persists, try using a different cable.
Getting rid of the ‘PC isn’t charging’ error notification
This error notification is possibly caused by the following:
- You’ve used an incompatible charger.
- You’ve used a charger with lower power limits, preventing it from properly charging your device or computer.
- You’ve incorrectly connected the charger to the port on your PC.
- The cable’s power capacity cannot accommodate the charger.
- The USB ports are dusty or dirty, preventing proper insertion of the charger.
- You’ve connected the charger through an external hub or dock.
You can fix USB-C compatibility issues by using the charger and cable that came with your device’s or computer’s packaging. You can also use compressed air to clean the ports, enabling you to insert the dongle correctly.
Resolving ‘The USB device might not work’ error
This error notification shows up when the Windows version on your PC does not support the driver for the device you’re trying to connect to the USB-C port. So, the solution to this is to install all the latest updates for your operating system. You can do this by following the instructions below:
- Click the Search icon on your taskbar.
- Type “settings” (no quotes), then hit Enter.
- Select Update & Security.
- Click Check for Updates.
- Install the available updates.
How to fix ‘These two devices can’t communicate’ error
You will see this error notification will show up when you are having trouble connecting two devices via USB-C. It is possible that one or both of the devices do not support the USB-C connection type. The workaround here is ensuring that you are connecting two Windows computers.
Resolving the error ‘USB device might not be working properly’
If your computer does not support the device you’re trying to connect via USB-C, you will see this error message. It is also possible that the power on your laptop is limited because you’re sourcing it from your battery. In this case, you can try using a different computer, or you can try plugging your device into an external power source.
What to do when you get a ‘Use a different USB port’ prompt
When you get this error notification, it is likely that the USB port does not support Thunderbolt, DisplayPort, or MHL. If this is the case, then you can try using a different port on your PC. It is also possible that the functionality of the USB device had become limited when you connected it to a particular port. You can try plugging it to a different port on your computer to resolve the problem.
Resolving the error ‘USB or Thunderbolt device functionality might be limited’
The reasons behind this error notification are similar to what caused the limited display connection issues. So, you can resolve this by making sure that your PC and cable support the same USB-C features as the device you’re trying to connect. You also have to make sure that the dongle is directly connected to your computer.
Which connection type do you prefer?
Let us know in the comments below!
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The world of PCI is vast and full of (mostly unpleasant) surprises.Since each CPU architecture implements different chip-sets and PCI deviceshave different requirements (erm, “features”), the result is the PCI supportin the Linux kernel is not as trivial as one would wish. This short papertries to introduce all potential driver authors to Linux APIs forPCI device drivers.
A more complete resource is the third edition of “Linux Device Drivers”by Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman.LDD3 is available for free (under Creative Commons License) from:https://lwn.net/Kernel/LDD3/.
However, keep in mind that all documents are subject to “bit rot”.Refer to the source code if things are not working as described here.
Please send questions/comments/patches about Linux PCI API to the“Linux PCI” <linux-pci@atrey.karlin.mff.cuni.cz> mailing list.
1.1. Structure of PCI drivers¶
PCI drivers “discover” PCI devices in a system via pci_register_driver().Actually, it’s the other way around. When the PCI generic code discoversa new device, the driver with a matching “description” will be notified.Details on this below.
pci_register_driver() leaves most of the probing for devices tothe PCI layer and supports online insertion/removal of devices [thussupporting hot-pluggable PCI, CardBus, and Express-Card in a single driver].pci_register_driver() call requires passing in a table of functionpointers and thus dictates the high level structure of a driver.
Once the driver knows about a PCI device and takes ownership, thedriver generally needs to perform the following initialization:
- Enable the device
- Request MMIO/IOP resources
- Set the DMA mask size (for both coherent and streaming DMA)
- Allocate and initialize shared control data (pci_allocate_coherent())
- Access device configuration space (if needed)
- Register IRQ handler (
request_irq()) - Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip)
- Enable DMA/processing engines
When done using the device, and perhaps the module needs to be unloaded,the driver needs to take the follow steps:
- Disable the device from generating IRQs
- Release the IRQ (
free_irq()) - Stop all DMA activity
- Release DMA buffers (both streaming and coherent)
- Unregister from other subsystems (e.g. scsi or netdev)
- Release MMIO/IOP resources
- Disable the device
Most of these topics are covered in the following sections.For the rest look at LDD3 or <linux/pci.h> .
If the PCI subsystem is not configured (CONFIG_PCI is not set), most ofthe PCI functions described below are defined as inline functions eithercompletely empty or just returning an appropriate error codes to avoidlots of ifdefs in the drivers.
1.2. pci_register_driver() call¶
PCI device drivers call pci_register_driver() during theirinitialization with a pointer to a structure describing the driver(structpci_driver):
pci_driver¶PCI driver structure
Definition
Members
node- List of driver structures.
name- Driver name.
id_table- Pointer to table of device IDs the driver isinterested in. Most drivers should export thistable using MODULE_DEVICE_TABLE(pci,…).
probe- This probing function gets called (during executionof pci_register_driver() for already existingdevices or later if a new device gets inserted) forall PCI devices which match the ID table and are not“owned” by the other drivers yet. This function getspassed a “struct pci_dev *” for each device whoseentry in the ID table matches the device. The probefunction returns zero when the driver chooses totake “ownership” of the device or an error code(negative number) otherwise.The probe function always gets called from processcontext, so it can sleep.
remove- The remove() function gets called whenever a devicebeing handled by this driver is removed (either duringderegistration of the driver or when it’s manuallypulled out of a hot-pluggable slot).The remove function always gets called from processcontext, so it can sleep.
suspend- Put device into low power state.
resume- Wake device from low power state.(Please see PCI Power Management for descriptionsof PCI Power Management and the related functions.)
shutdown- Hook into reboot_notifier_list (kernel/sys.c).Intended to stop any idling DMA operations.Useful for enabling wake-on-lan (NIC) or changingthe power state of a device before reboot.e.g. drivers/net/e100.c.
sriov_configure- Optional driver callback to allow configuration ofnumber of VFs to enable via sysfs “sriov_numvfs” file.
err_handler- See PCI Error Recovery
groups- Sysfs attribute groups.
driver- Driver model structure.
dynids- List of dynamically added device IDs.
The ID table is an array of structpci_device_id entries ending with anall-zero entry. Definitions with static const are generally preferred.
pci_device_id¶PCI device ID structure
Definition
Members
vendor- Vendor ID to match (or PCI_ANY_ID)
device- Device ID to match (or PCI_ANY_ID)
subvendor- Subsystem vendor ID to match (or PCI_ANY_ID)
subdevice- Subsystem device ID to match (or PCI_ANY_ID)
class- Device class, subclass, and “interface” to match.See Appendix D of the PCI Local Bus Spec orinclude/linux/pci_ids.h for a full list of classes.Most drivers do not need to specify class/class_maskas vendor/device is normally sufficient.
class_mask- Limit which sub-fields of the class field are compared.See drivers/scsi/sym53c8xx_2/ for example of usage.
driver_data- Data private to the driver.Most drivers don’t need to use driver_data field.Best practice is to use driver_data as an indexinto a static list of equivalent device types,instead of using it as a pointer.
Most drivers only need PCI_DEVICE() or PCI_DEVICE_CLASS() to set upa pci_device_id table.
New PCI IDs may be added to a device driver pci_ids table at runtimeas shown below:
All fields are passed in as hexadecimal values (no leading 0x).The vendor and device fields are mandatory, the others are optional. Usersneed pass only as many optional fields as necessary:
- subvendor and subdevice fields default to PCI_ANY_ID (FFFFFFFF)
- class and classmask fields default to 0
- driver_data defaults to 0UL.
Note that driver_data must match the value used by any of the pci_device_identries defined in the driver. This makes the driver_data field mandatoryif all the pci_device_id entries have a non-zero driver_data value.
Once added, the driver probe routine will be invoked for any unclaimedPCI devices listed in its (newly updated) pci_ids list.
When the driver exits, it just calls pci_unregister_driver() and the PCI layerautomatically calls the remove hook for all devices handled by the driver.
1.2.1. “Attributes” for driver functions/data¶
Please mark the initialization and cleanup functions where appropriate(the corresponding macros are defined in <linux/init.h>):
| __init | Initialization code. Thrown away after the driverinitializes. |
| __exit | Exit code. Ignored for non-modular drivers. |
- The
module_init()/module_exit()functions (and allinitialization functions called _only_ from these)should be marked __init/__exit. - Do not mark the
structpci_driver. - Do NOT mark a function if you are not sure which mark to use.Better to not mark the function than mark the function wrong.
1.3. How to find PCI devices manually¶
PCI drivers should have a really good reason for not using thepci_register_driver() interface to search for PCI devices.The main reason PCI devices are controlled by multiple driversis because one PCI device implements several different HW services.E.g. combined serial/parallel port/floppy controller.
A manual search may be performed using the following constructs:
Searching by vendor and device ID:
Searching by class ID (iterate in a similar way):
Searching by both vendor/device and subsystem vendor/device ID:
You can use the constant PCI_ANY_ID as a wildcard replacement forVENDOR_ID or DEVICE_ID. This allows searching for any device from aspecific vendor, for example.
These functions are hotplug-safe. They increment the reference count onthe pci_dev that they return. You must eventually (possibly at module unload)decrement the reference count on these devices by calling pci_dev_put().
1.4. Device Initialization Steps¶
As noted in the introduction, most PCI drivers need the following stepsfor device initialization:
- Enable the device
- Request MMIO/IOP resources
- Set the DMA mask size (for both coherent and streaming DMA)
- Allocate and initialize shared control data (pci_allocate_coherent())
- Access device configuration space (if needed)
- Register IRQ handler (
request_irq()) - Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip)
- Enable DMA/processing engines.
The driver can access PCI config space registers at any time.(Well, almost. When running BIST, config space can go away…butthat will just result in a PCI Bus Master Abort and config readswill return garbage).
1.4.1. Enable the PCI device¶
Before touching any device registers, the driver needs to enablethe PCI device by calling pci_enable_device(). This will:
- wake up the device if it was in suspended state,
- allocate I/O and memory regions of the device (if BIOS did not),
- allocate an IRQ (if BIOS did not).
Note
pci_enable_device() can fail! Check the return value.
Warning
OS BUG: we don’t check resource allocations before enabling thoseresources. The sequence would make more sense if we calledpci_request_resources() before calling pci_enable_device().Currently, the device drivers can’t detect the bug when twodevices have been allocated the same range. This is not a commonproblem and unlikely to get fixed soon.
This has been discussed before but not changed as of 2.6.19:https://lore.kernel.org/r/20060302180025.GC28895@flint.arm.linux.org.uk/
pci_set_master() will enable DMA by setting the bus master bitin the PCI_COMMAND register. It also fixes the latency timer value ifit’s set to something bogus by the BIOS. pci_clear_master() willdisable DMA by clearing the bus master bit.
If the PCI device can use the PCI Memory-Write-Invalidate transaction,call pci_set_mwi(). This enables the PCI_COMMAND bit for Mem-Wr-Invaland also ensures that the cache line size register is set correctly.Check the return value of pci_set_mwi() as not all architecturesor chip-sets may support Memory-Write-Invalidate. Alternatively,if Mem-Wr-Inval would be nice to have but is not required, callpci_try_set_mwi() to have the system do its best effort at enablingMem-Wr-Inval.
1.4.2. Request MMIO/IOP resources¶
Memory (MMIO), and I/O port addresses should NOT be read directlyfrom the PCI device config space. Use the values in the pci_dev structureas the PCI “bus address” might have been remapped to a “host physical”address by the arch/chip-set specific kernel support.
See The io_mapping functions for how to access device registersor device memory.
The device driver needs to call pci_request_region() to verifyno other device is already using the same address resource.Conversely, drivers should call pci_release_region() AFTERcalling pci_disable_device().The idea is to prevent two devices colliding on the same address range.
Tip
See OS BUG comment above. Currently (2.6.19), The driver can onlydetermine MMIO and IO Port resource availability _after_ callingpci_enable_device().
Generic flavors of pci_request_region() are request_mem_region()(for MMIO ranges) and request_region() (for IO Port ranges).Use these for address resources that are not described by “normal” PCIBARs.
Also see pci_request_selected_regions() below.
1.4.3. Set the DMA mask size¶
Note
If anything below doesn’t make sense, please refer toDynamic DMA mapping using the generic device. This section is just a reminder thatdrivers need to indicate DMA capabilities of the device and is notan authoritative source for DMA interfaces.
While all drivers should explicitly indicate the DMA capability(e.g. 32 or 64 bit) of the PCI bus master, devices with more than32-bit bus master capability for streaming data need the driverto “register” this capability by calling pci_set_dma_mask() withappropriate parameters. In general this allows more efficient DMAon systems where System RAM exists above 4G _physical_ address.
Fwp Port Devices Driver Device
Drivers for all PCI-X and PCIe compliant devices must callpci_set_dma_mask() as they are 64-bit DMA devices.
Similarly, drivers must also “register” this capability if the devicecan directly address “consistent memory” in System RAM above 4G physicaladdress by calling pci_set_consistent_dma_mask().Again, this includes drivers for all PCI-X and PCIe compliant devices.Many 64-bit “PCI” devices (before PCI-X) and some PCI-X devices are64-bit DMA capable for payload (“streaming”) data but not control(“consistent”) data.
1.4.4. Setup shared control data¶
Once the DMA masks are set, the driver can allocate “consistent” (a.k.a. shared)memory. See Dynamic DMA mapping using the generic device for a full description ofthe DMA APIs. This section is just a reminder that it needs to be donebefore enabling DMA on the device.
1.4.5. Initialize device registers¶
Some drivers will need specific “capability” fields programmedor other “vendor specific” register initialized or reset.E.g. clearing pending interrupts.
1.4.6. Register IRQ handler¶
While calling request_irq() is the last step described here,this is often just another intermediate step to initialize a device.This step can often be deferred until the device is opened for use.
All interrupt handlers for IRQ lines should be registered with IRQF_SHAREDand use the devid to map IRQs to devices (remember that all PCI IRQ linescan be shared).
request_irq() will associate an interrupt handler and device handlewith an interrupt number. Historically interrupt numbers representIRQ lines which run from the PCI device to the Interrupt controller.With MSI and MSI-X (more below) the interrupt number is a CPU “vector”.
request_irq() also enables the interrupt. Make sure the device isquiesced and does not have any interrupts pending before registeringthe interrupt handler.
MSI and MSI-X are PCI capabilities. Both are “Message Signaled Interrupts”which deliver interrupts to the CPU via a DMA write to a Local APIC.The fundamental difference between MSI and MSI-X is how multiple“vectors” get allocated. MSI requires contiguous blocks of vectorswhile MSI-X can allocate several individual ones.
MSI capability can be enabled by calling pci_alloc_irq_vectors() with thePCI_IRQ_MSI and/or PCI_IRQ_MSIX flags before calling request_irq(). Thiscauses the PCI support to program CPU vector data into the PCI devicecapability registers. Many architectures, chip-sets, or BIOSes do NOTsupport MSI or MSI-X and a call to pci_alloc_irq_vectors with justthe PCI_IRQ_MSI and PCI_IRQ_MSIX flags will fail, so try to alwaysspecify PCI_IRQ_LEGACY as well.
Fwp Port Devices Driver Ed
Drivers that have different interrupt handlers for MSI/MSI-X andlegacy INTx should chose the right one based on the msi_enabledand msix_enabled flags in the pci_dev structure after callingpci_alloc_irq_vectors.
There are (at least) two really good reasons for using MSI:
- MSI is an exclusive interrupt vector by definition.This means the interrupt handler doesn’t have to verifyits device caused the interrupt.
- MSI avoids DMA/IRQ race conditions. DMA to host memory is guaranteedto be visible to the host CPU(s) when the MSI is delivered. Thisis important for both data coherency and avoiding stale control data.This guarantee allows the driver to omit MMIO reads to flushthe DMA stream.
See drivers/infiniband/hw/mthca/ or drivers/net/tg3.c for examplesof MSI/MSI-X usage.
1.5. PCI device shutdown¶
When a PCI device driver is being unloaded, most of the followingsteps need to be performed:
- Disable the device from generating IRQs
- Release the IRQ (
free_irq()) - Stop all DMA activity
- Release DMA buffers (both streaming and consistent)
- Unregister from other subsystems (e.g. scsi or netdev)
- Disable device from responding to MMIO/IO Port addresses
- Release MMIO/IO Port resource(s)
1.5.1. Stop IRQs on the device¶
How to do this is chip/device specific. If it’s not done, it opensthe possibility of a “screaming interrupt” if (and only if)the IRQ is shared with another device.
When the shared IRQ handler is “unhooked”, the remaining devicesusing the same IRQ line will still need the IRQ enabled. Thus if the“unhooked” device asserts IRQ line, the system will respond assumingit was one of the remaining devices asserted the IRQ line. Since noneof the other devices will handle the IRQ, the system will “hang” untilit decides the IRQ isn’t going to get handled and masks the IRQ (100,000iterations later). Once the shared IRQ is masked, the remaining deviceswill stop functioning properly. Not a nice situation.
This is another reason to use MSI or MSI-X if it’s available.MSI and MSI-X are defined to be exclusive interrupts and thusare not susceptible to the “screaming interrupt” problem.
1.5.2. Release the IRQ¶
Once the device is quiesced (no more IRQs), one can call free_irq().This function will return control once any pending IRQs are handled,“unhook” the drivers IRQ handler from that IRQ, and finally releasethe IRQ if no one else is using it.
1.5.3. Stop all DMA activity¶
It’s extremely important to stop all DMA operations BEFORE attemptingto deallocate DMA control data. Failure to do so can result in memorycorruption, hangs, and on some chip-sets a hard crash.
Stopping DMA after stopping the IRQs can avoid races where theIRQ handler might restart DMA engines.
While this step sounds obvious and trivial, several “mature” driversdidn’t get this step right in the past.
1.5.4. Release DMA buffers¶
Once DMA is stopped, clean up streaming DMA first.I.e. unmap data buffers and return buffers to “upstream”owners if there is one.
Then clean up “consistent” buffers which contain the control data.
See Dynamic DMA mapping using the generic device for details on unmapping interfaces.
1.5.5. Unregister from other subsystems¶
Most low level PCI device drivers support some other subsystemlike USB, ALSA, SCSI, NetDev, Infiniband, etc. Make sure yourdriver isn’t losing resources from that other subsystem.If this happens, typically the symptom is an Oops (panic) whenthe subsystem attempts to call into a driver that has been unloaded.
1.5.6. Disable Device from responding to MMIO/IO Port addresses¶
io_unmap() MMIO or IO Port resources and then call pci_disable_device().This is the symmetric opposite of pci_enable_device().Do not access device registers after calling pci_disable_device().
1.5.7. Release MMIO/IO Port Resource(s)¶
Call pci_release_region() to mark the MMIO or IO Port range as available.Failure to do so usually results in the inability to reload the driver.
1.6. How to access PCI config space¶
You can use pci_(read|write)_config_(byte|word|dword) to access the configspace of a device represented by struct pci_dev *. All these functions return0 when successful or an error code (PCIBIOS_…) which can be translated to atext string by pcibios_strerror. Most drivers expect that accesses to valid PCIdevices don’t fail.
If you don’t have a struct pci_dev available, you can callpci_bus_(read|write)_config_(byte|word|dword) to access a given deviceand function on that bus.
If you access fields in the standard portion of the config header, pleaseuse symbolic names of locations and bits declared in <linux/pci.h>.
If you need to access Extended PCI Capability registers, just callpci_find_capability() for the particular capability and it will find thecorresponding register block for you.
1.7. Other interesting functions¶
pci_get_domain_bus_and_slot() | Find pci_dev corresponding to given domain,bus and slot and number. If the device isfound, its reference count is increased. |
pci_set_power_state() | Set PCI Power Management state (0=D0 … 3=D3) |
pci_find_capability() | Find specified capability in device’s capabilitylist. |
| pci_resource_start() | Returns bus start address for a given PCI region |
| pci_resource_end() | Returns bus end address for a given PCI region |
| pci_resource_len() | Returns the byte length of a PCI region |
| pci_set_drvdata() | Set private driver data pointer for a pci_dev |
| pci_get_drvdata() | Return private driver data pointer for a pci_dev |
pci_set_mwi() | Enable Memory-Write-Invalidate transactions. |
pci_clear_mwi() | Disable Memory-Write-Invalidate transactions. |
1.8. Miscellaneous hints¶
When displaying PCI device names to the user (for example when a driver wantsto tell the user what card has it found), please use pci_name(pci_dev).
Always refer to the PCI devices by a pointer to the pci_dev structure.All PCI layer functions use this identification and it’s the onlyreasonable one. Don’t use bus/slot/function numbers except for veryspecial purposes – on systems with multiple primary buses their semanticscan be pretty complex.
Don’t try to turn on Fast Back to Back writes in your driver. All deviceson the bus need to be capable of doing it, so this is something which needsto be handled by platform and generic code, not individual drivers.
1.9. Vendor and device identifications¶
Do not add new device or vendor IDs to include/linux/pci_ids.h unless theyare shared across multiple drivers. You can add private definitions inyour driver if they’re helpful, or just use plain hex constants.
The device IDs are arbitrary hex numbers (vendor controlled) and normally usedonly in a single location, the pci_device_id table.
Please DO submit new vendor/device IDs to https://pci-ids.ucw.cz/.There’s a mirror of the pci.ids file at https://github.com/pciutils/pciids.
1.10. Obsolete functions¶
There are several functions which you might come across when trying toport an old driver to the new PCI interface. They are no longer presentin the kernel as they aren’t compatible with hotplug or PCI domains orhaving sane locking.
| pci_find_device() | Superseded by pci_get_device() |
| pci_find_subsys() | Superseded by pci_get_subsys() |
| pci_find_slot() | Superseded by pci_get_domain_bus_and_slot() |
pci_get_slot() | Superseded by pci_get_domain_bus_and_slot() |
The alternative is the traditional PCI device driver that walks PCIdevice lists. This is still possible but discouraged.
1.11. MMIO Space and “Write Posting”¶
Converting a driver from using I/O Port space to using MMIO spaceoften requires some additional changes. Specifically, “write posting”needs to be handled. Many drivers (e.g. tg3, acenic, sym53c8xx_2)already do this. I/O Port space guarantees write transactions reach the PCIdevice before the CPU can continue. Writes to MMIO space allow the CPUto continue before the transaction reaches the PCI device. HW weeniescall this “Write Posting” because the write completion is “posted” tothe CPU before the transaction has reached its destination.
Thus, timing sensitive code should add readl() where the CPU isexpected to wait before doing other work. The classic “bit banging”sequence works fine for I/O Port space:
The same sequence for MMIO space should be:
It is important that “safe_mmio_reg” not have any side effects thatinterferes with the correct operation of the device.
Another case to watch out for is when resetting a PCI device. Use PCIConfiguration space reads to flush the writel(). This will gracefullyhandle the PCI master abort on all platforms if the PCI device isexpected to not respond to a readl(). Most x86 platforms will allowMMIO reads to master abort (a.k.a. “Soft Fail”) and return garbage(e.g. ~0). But many RISC platforms will crash (a.k.a.”Hard Fail”).