How to disable a plugged-in PCI-e graphic card on OS level? [duplicate]
I have a server running for which I want to have a possility to access it with a screen connected to VGA (very rarely, most of the time it’s accessed via SSH). Therefore I have a PCI-e graphic cards plugged in and the VGA cable removed. The graphic card is passively cooled and if I open the case and touch the cool body I can feel a noticable warmth and conclue that it’s consuming energy (there’re no consumers close to it that could transmit the thermal energy in any way).
If I unplug the card (as suggested in Should I Disable an unused graphic card?) I have to built it in every time I want to connect a screen. I would like to avoid that as well as the energy consumption.
The de- and re-activation needs to take place on the OS level (e.g. via SSH) because otherwise I’d need a screen to configure the UEFI (or do that blindly which is no alternative) and run into a chicken-egg-problem.
I’m using Ubuntu 15.04 with Linux 4.0.2. The graphic card is labeled XFX HD 5450 850M and has a VGA, HDMI and D-SUB connector. The mainboard is an ASRock X99-Extreme without integrated graphic.
EDIT: After blacklisting used modules listed in sudo lspci -v (following @WhimsicalWombat’s promising answer below) (in my case I had to use the modprobe.blacklist=module_to_blacklist kernel parameter — see https://askubuntu.com/questions/110341/how-to-blacklist-kernel-modules for more details — for radeon and snd_hda_intel ) the PCIe graphic card still heats up (passive cooler has > 60 degrees and there’s no heat source closeby) and no modules are listed in lspci -v for the devices. The output of lspci -v for the devices is not
EDIT 2: https://askubuntu.com/a/138953/173287 suggests to do echo 0 > /sys/bus/pci/slots/$N/power and I have a /sys/bus/pci/slots/$N where $N is number of the slot listed in lspci -v , but there’s no power file.
EDIT 3: adding the modaliases of /sys/bus/pci/devices/[device]/modalias to modprobe.blacklist= kernel parameters has no effect on Ubuntu mainline kernels from http://kernel.ubuntu.com/
kernel-ppa/mainline/ and a custom 4.0.5 build with make localmodconfig and activation of all PCI options causes the «Loading initramfs [version]» screen to remain visible for ever while the graphic card is still heating up.
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Получится ли отключить PCI Express видеокарту средствами линукс?
Есть ПК, в нем дуалбут с арчлинуксом и виндой. Думаю купить норм видеокарту для учебы поиграть в винде. А в линуксе достаточно и интегрированной интел.
План такой: в монитор воткнуть 2 кабеля — с PCI и интел видеокарт. В винде отключить интел. В линуксе — наоборот, PCI. В общем, чтобы дуалбутиться без перетыкивания кабелей.
Вопрос. Возможно ли настроить, чтоб при загрузке в линукс, PCI видеокарта отключалась? А именно, не грелась и не запускала пропеллеры? И какую видюху лучше взять чтобы такое проще было осуществить (используя только свободные драйвера). Особых предпочтений к nvidia или amd не имею. Подойдет любая.
man vt-d, IOMMU, vga passthrough
Я кстати успешно так последний дум прошел в qemu с этой штукой
Мне не нужна мощная видюха в линуксе впринципе. Вопрос не про это
Мне не нужна мощная видюха в линуксе впринципе.
Чем она тебе мешает? Всё равно ты её нормально не отключишь. Максимум будет жрать больше электричества и чаще включать вентиляторы без загруженного драйвера.
Тем что греется и шумит? В линуксе мне нужна только интегрированная интел
Всё равно ты её нормально не отключишь
Вообще никак? Неужели всё так печально
решил БУ взять ? Вообще современные умеют отключать крутиляторы на низкой нагрузке, ну или можно кривую настроить. Если ты на нее видео не выводишь, греться ей незачем
Возможно ли настроить, чтоб при загрузке в линукс, PCI видеокарта отключалась? А именно, не грелась и не запускала пропеллеры?
не скажу про конкретные карточки, думаю от драйвера всё зависит. делается это как-то так:
# echo ‘выключить ня!’ > ‘/sys/bus/pci/devices/ /power/control’
т.е. не стоит выбрасывать (из ядра) драйвер карточки в данном случае. остаётся лишь погуглить функции управления питанием в nouveau, radeon и nvidia.
p.s.: кстати, когда ты в винде «отключаешь» в device manager-е железку, далеко не факт, что ты этим перекрываешь питание. иначе hot swap в M$ работал бы на ура, в отличие от..
Вообще современные умеют отключать крутиляторы на низкой нагрузке
Ну не знаю. Стояла Radeon R7. В линуксе жужжала непрекращая
# echo ‘выключить ня!’ > ‘/sys/bus/pci/devices/ /power/control’
Вот этот момент и интересует. Может есть у кого реальные истории успеха
кстати, когда ты в винде «отключаешь» в device manager-е железку, далеко не факт, что ты этим перекрываешь питание
Да на интеграшку пофиг, впринципе. Пусть работает. Не шумит и ладно
у меня RX480. Из коробки в линуксе кривая крутиляторов отличается от офтопика. Более щадящая. Я не стал менять ибо корпус хороший и сами крутиляторы достаточно тихие, как оно ведет себя с IOMMU=on могу потом сказать
Из коробки в линуксе кривая крутиляторов отличается от офтопика. Более щадящая
То-есть таки крутит вентиляторы в покое? 99% времени я в линуксе и пара лишних пропеллеров под столом мне нафиг не нужны. Хотелось бы отключить ее вообще в линуксе
но так ведь можно не дуалбутится и в игры играть и в линуксе работать..
в арче есть пакет для отрубания дискретки думаю можно расковырять и в бут поставить.. https://wiki.archlinux.org/index.php/hybrid_graphics
Если повезёт, echo OFF > /sys/kernel/debug/vgaswitcheroo/switch отключит дискретную видеокарту. Насколько я знаю, это сильно зависит от кода в ACPI. В ноутбуках код для отключения прописывают. В настольном такого может не быть.
То-есть таки крутит вентиляторы в покое?
так возьми да поменяй. В арче например есть какая-та утилита для амуды, для зеленых не знаю.
Из коробки в линуксе кривая крутиляторов отличается от офтопика. Более щадящая.
Ты уверен, что не прямая? Покажи /sys/class/drm/card0/device/hwmon/hwmon1/pwm1 Просто оно сломано (как я понял по коду — не сделано) в ядре, и автоматическая регулировка в соответствии с «кривой» в прошивке карты не включается.
vfio-pci же
настрой видяху, чтобы она использовала драйвер vfio-pci. Думаю, это то, что ты хочешь.
Starting with Linux 4.1, the kernel includes vfio-pci, which is functionally similar to pci-stub with a few added bonuses, such as switching devices into their D3 state when they are not in use.
Можно заменить дуалбут на qemu и «vt-d, IOMMU, vga passthrough», как писали выше, но это необязательно.
Не думал что всё так плохо. Тогда вообще ничего покупать и играть не буду )
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Disable pci device linux
The world of PCI is vast and full of (mostly unpleasant) surprises. Since each CPU architecture implements different chip-sets and PCI devices have different requirements (erm, «features»), the result is the PCI support in the Linux kernel is not as trivial as one would wish. This short paper tries to introduce all potential driver authors to Linux APIs for PCI 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: http://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»
mailing list. 0. 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 discovers a 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 to the PCI layer and supports online insertion/removal of devices [thus supporting hot-pluggable PCI, CardBus, and Express-Card in a single driver]. pci_register_driver() call requires passing in a table of function pointers and thus dictates the high level structure of a driver. Once the driver knows about a PCI device and takes ownership, the driver 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
. If the PCI subsystem is not configured (CONFIG_PCI is not set), most of the PCI functions described below are defined as inline functions either completely empty or just returning an appropriate error codes to avoid lots of ifdefs in the drivers. 1. pci_register_driver() call
PCI device drivers call pci_register_driver() during their initialization with a pointer to a structure describing the driver (struct pci_driver): field name Description ———- —————————————————— id_table Pointer to table of device ID’s the driver is interested in. Most drivers should export this table using MODULE_DEVICE_TABLE(pci. ). probe This probing function gets called (during execution of pci_register_driver() for already existing devices or later if a new device gets inserted) for all PCI devices which match the ID table and are not «owned» by the other drivers yet. This function gets passed a «struct pci_dev *» for each device whose entry in the ID table matches the device. The probe function returns zero when the driver chooses to take «ownership» of the device or an error code (negative number) otherwise. The probe function always gets called from process context, so it can sleep. remove The remove() function gets called whenever a device being handled by this driver is removed (either during deregistration of the driver or when it’s manually pulled out of a hot-pluggable slot). The remove function always gets called from process context, so it can sleep. suspend Put device into low power state. suspend_late Put device into low power state. resume_early Wake device from low power state. resume Wake device from low power state. (Please see Documentation/power/pci.txt for descriptions of 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 changing the power state of a device before reboot. e.g. drivers/net/e100.c. err_handler See Documentation/PCI/pci-error-recovery.txt The ID table is an array of struct pci_device_id entries ending with an all-zero entry. Definitions with static const are generally preferred. Each entry consists of: vendor,device Vendor and device ID to match (or PCI_ANY_ID) subvendor, Subsystem vendor and device ID to match (or PCI_ANY_ID) subdevice, class Device class, subclass, and «interface» to match. See Appendix D of the PCI Local Bus Spec or include/linux/pci_ids.h for a full list of classes. Most drivers do not need to specify class/class_mask as 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 index into 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 up a pci_device_id table. New PCI IDs may be added to a device driver pci_ids table at runtime as shown below: echo «vendor device subvendor subdevice class class_mask driver_data» > \ /sys/bus/pci/drivers/
): __init Initialization code. Thrown away after the driver initializes. __exit Exit code. Ignored for non-modular drivers. Tips on when/where to use the above attributes: o The module_init()/module_exit() functions (and all initialization functions called _only_ from these) should be marked __init/__exit. o Do not mark the struct pci_driver. o 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. 2. How to find PCI devices manually
PCI drivers should have a really good reason for not using the pci_register_driver() interface to search for PCI devices. The main reason PCI devices are controlled by multiple drivers is 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: struct pci_dev *dev = NULL; while (dev = pci_get_device(VENDOR_ID, DEVICE_ID, dev)) configure_device(dev); Searching by class ID (iterate in a similar way): pci_get_class(CLASS_ID, dev) Searching by both vendor/device and subsystem vendor/device ID: pci_get_subsys(VENDOR_ID,DEVICE_ID, SUBSYS_VENDOR_ID, SUBSYS_DEVICE_ID, dev). You can use the constant PCI_ANY_ID as a wildcard replacement for VENDOR_ID or DEVICE_ID. This allows searching for any device from a specific vendor, for example. These functions are hotplug-safe. They increment the reference count on the pci_dev that they return. You must eventually (possibly at module unload) decrement the reference count on these devices by calling pci_dev_put(). 3. Device Initialization Steps
As noted in the introduction, most PCI drivers need the following steps for 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. but that will just result in a PCI Bus Master Abort and config reads will return garbage). 3.1 Enable the PCI device
Before touching any device registers, the driver needs to enable the PCI device by calling pci_enable_device(). This will: o wake up the device if it was in suspended state, o allocate I/O and memory regions of the device (if BIOS did not), o allocate an IRQ (if BIOS did not). NOTE: pci_enable_device() can fail! Check the return value. [ OS BUG: we don’t check resource allocations before enabling those resources. The sequence would make more sense if we called pci_request_resources() before calling pci_enable_device(). Currently, the device drivers can’t detect the bug when when two devices have been allocated the same range. This is not a common problem and unlikely to get fixed soon. This has been discussed before but not changed as of 2.6.19: http://lkml.org/lkml/2006/3/2/194 ] pci_set_master() will enable DMA by setting the bus master bit in the PCI_COMMAND register. It also fixes the latency timer value if it’s set to something bogus by the BIOS. pci_clear_master() will disable 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-Inval and also ensures that the cache line size register is set correctly. Check the return value of pci_set_mwi() as not all architectures or chip-sets may support Memory-Write-Invalidate. Alternatively, if Mem-Wr-Inval would be nice to have but is not required, call pci_try_set_mwi() to have the system do its best effort at enabling Mem-Wr-Inval. 3.2 Request MMIO/IOP resources
Memory (MMIO), and I/O port addresses should NOT be read directly from the PCI device config space. Use the values in the pci_dev structure as the PCI «bus address» might have been remapped to a «host physical» address by the arch/chip-set specific kernel support. See Documentation/io-mapping.txt for how to access device registers or device memory. The device driver needs to call pci_request_region() to verify no other device is already using the same address resource. Conversely, drivers should call pci_release_region() AFTER calling pci_disable_device(). The idea is to prevent two devices colliding on the same address range. [ See OS BUG comment above. Currently (2.6.19), The driver can only determine MMIO and IO Port resource availability _after_ calling pci_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» PCI BARs. Also see pci_request_selected_regions() below. 3.3 Set the DMA mask size
[ If anything below doesn’t make sense, please refer to Documentation/DMA-API.txt. This section is just a reminder that drivers need to indicate DMA capabilities of the device and is not an 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 than 32-bit bus master capability for streaming data need the driver to «register» this capability by calling pci_set_dma_mask() with appropriate parameters. In general this allows more efficient DMA on systems where System RAM exists above 4G _physical_ address. Drivers for all PCI-X and PCIe compliant devices must call pci_set_dma_mask() as they are 64-bit DMA devices. Similarly, drivers must also «register» this capability if the device can directly address «consistent memory» in System RAM above 4G physical address 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 are 64-bit DMA capable for payload («streaming») data but not control («consistent») data. 3.4 Setup shared control data
Once the DMA masks are set, the driver can allocate «consistent» (a.k.a. shared) memory. See Documentation/DMA-API.txt for a full description of the DMA APIs. This section is just a reminder that it needs to be done before enabling DMA on the device. 3.5 Initialize device registers
Some drivers will need specific «capability» fields programmed or other «vendor specific» register initialized or reset. E.g. clearing pending interrupts. 3.6 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_SHARED and use the devid to map IRQs to devices (remember that all PCI IRQ lines can be shared). request_irq() will associate an interrupt handler and device handle with an interrupt number. Historically interrupt numbers represent IRQ 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 is quiesced and does not have any interrupts pending before registering the 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 vectors while MSI-X can allocate several individual ones. MSI capability can be enabled by calling pci_alloc_irq_vectors() with the PCI_IRQ_MSI and/or PCI_IRQ_MSIX flags before calling request_irq(). This causes the PCI support to program CPU vector data into the PCI device capability registers. Many architectures, chip-sets, or BIOSes do NOT support MSI or MSI-X and a call to pci_alloc_irq_vectors with just the PCI_IRQ_MSI and PCI_IRQ_MSIX flags will fail, so try to always specify PCI_IRQ_LEGACY as well. Drivers that have different interrupt handlers for MSI/MSI-X and legacy INTx should chose the right one based on the msi_enabled and msix_enabled flags in the pci_dev structure after calling pci_alloc_irq_vectors. There are (at least) two really good reasons for using MSI: 1) MSI is an exclusive interrupt vector by definition. This means the interrupt handler doesn’t have to verify its device caused the interrupt. 2) MSI avoids DMA/IRQ race conditions. DMA to host memory is guaranteed to be visible to the host CPU(s) when the MSI is delivered. This is important for both data coherency and avoiding stale control data. This guarantee allows the driver to omit MMIO reads to flush the DMA stream. See drivers/infiniband/hw/mthca/ or drivers/net/tg3.c for examples of MSI/MSI-X usage. 4. PCI device shutdown
When a PCI device driver is being unloaded, most of the following steps 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) 4.1 Stop IRQs on the device
How to do this is chip/device specific. If it’s not done, it opens the 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 devices using the same IRQ line will still need the IRQ enabled. Thus if the «unhooked» device asserts IRQ line, the system will respond assuming it was one of the remaining devices asserted the IRQ line. Since none of the other devices will handle the IRQ, the system will «hang» until it decides the IRQ isn’t going to get handled and masks the IRQ (100,000 iterations later). Once the shared IRQ is masked, the remaining devices will 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 thus are not susceptible to the «screaming interrupt» problem. 4.2 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 release the IRQ if no one else is using it. 4.3 Stop all DMA activity
It’s extremely important to stop all DMA operations BEFORE attempting to deallocate DMA control data. Failure to do so can result in memory corruption, hangs, and on some chip-sets a hard crash. Stopping DMA after stopping the IRQs can avoid races where the IRQ handler might restart DMA engines. While this step sounds obvious and trivial, several «mature» drivers didn’t get this step right in the past. 4.4 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 Documentation/DMA-API.txt for details on unmapping interfaces. 4.5 Unregister from other subsystems
Most low level PCI device drivers support some other subsystem like USB, ALSA, SCSI, NetDev, Infiniband, etc. Make sure your driver isn’t losing resources from that other subsystem. If this happens, typically the symptom is an Oops (panic) when the subsystem attempts to call into a driver that has been unloaded. 4.6 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(). 4.7 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. 5. How to access PCI config space
You can use pci_(read|write)_config_(byte|word|dword) to access the config space of a device represented by struct pci_dev *. All these functions return 0 when successful or an error code (PCIBIOS_. ) which can be translated to a text string by pcibios_strerror. Most drivers expect that accesses to valid PCI devices don’t fail. If you don’t have a struct pci_dev available, you can call pci_bus_(read|write)_config_(byte|word|dword) to access a given device and function on that bus. If you access fields in the standard portion of the config header, please use symbolic names of locations and bits declared in
. If you need to access Extended PCI Capability registers, just call pci_find_capability() for the particular capability and it will find the corresponding register block for you. 6. Other interesting functions
pci_get_domain_bus_and_slot() Find pci_dev corresponding to given domain, bus and slot and number. If the device is found, 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 capability list. 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. 7. Miscellaneous hints
When displaying PCI device names to the user (for example when a driver wants to 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 only reasonable one. Don’t use bus/slot/function numbers except for very special purposes — on systems with multiple primary buses their semantics can be pretty complex. Don’t try to turn on Fast Back to Back writes in your driver. All devices on the bus need to be capable of doing it, so this is something which needs to be handled by platform and generic code, not individual drivers. 8. Vendor and device identifications
Do not add new device or vendor IDs to include/linux/pci_ids.h unless they are shared across multiple drivers. You can add private definitions in your driver if they’re helpful, or just use plain hex constants. The device IDs are arbitrary hex numbers (vendor controlled) and normally used only in a single location, the pci_device_id table. Please DO submit new vendor/device IDs to http://pci-ids.ucw.cz/. There are mirrors of the pci.ids file at http://pciids.sourceforge.net/ and https://github.com/pciutils/pciids. 9. Obsolete functions
There are several functions which you might come across when trying to port an old driver to the new PCI interface. They are no longer present in the kernel as they aren’t compatible with hotplug or PCI domains or having 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 PCI device lists. This is still possible but discouraged. 10. MMIO Space and «Write Posting»
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