Re: [RFC, drm-misc-next v4 0/9] PCI/VGA: Allowing the user to select the primary video adapter at boot time

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 05.09.23 um 12:38 schrieb Jani Nikula:
> On Tue, 05 Sep 2023, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>> From: Sui Jingfeng <suijingfeng@loongson.cn>
>>
>> On a machine with multiple GPUs, a Linux user has no control over which
>> one is primary at boot time. This series tries to solve above mentioned
>> problem by introduced the ->be_primary() function stub. The specific
>> device drivers can provide an implementation to hook up with this stub by
>> calling the vga_client_register() function.
>>
>> Once the driver bound the device successfully, VGAARB will call back to
>> the device driver. To query if the device drivers want to be primary or
>> not. Device drivers can just pass NULL if have no such needs.
>>
>> Please note that:
>>
>> 1) The ARM64, Loongarch, Mips servers have a lot PCIe slot, and I would
>>     like to mount at least three video cards.

Well, you rarely find a board which can actually handle a single one :)

>>
>> 2) Typically, those non-86 machines don't have a good UEFI firmware
>>     support, which doesn't support select primary GPU as firmware stage.
>>     Even on x86, there are old UEFI firmwares which already made undesired
>>     decision for you.
>>
>> 3) This series is attempt to solve the remain problems at the driver level,
>>     while another series[1] of me is target to solve the majority of the
>>     problems at device level.
>>
>> Tested (limited) on x86 with four video card mounted, Intel UHD Graphics
>> 630 is the default boot VGA, successfully override by ast2400 with
>> ast.modeset=10 append at the kernel cmd line.
> The value 10 is incredibly arbitrary, and multiplied as a magic number
> all over the place.

+1

>
>> $ lspci | grep VGA
>>
>>   00:02.0 VGA compatible controller: Intel Corporation CoffeeLake-S GT2 [UHD Graphics 630]
>>   01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos XTX [Radeon HD 8490 / R5 235X OEM]
>>   04:00.0 VGA compatible controller: ASPEED Technology, Inc. ASPEED Graphics Family (rev 30)
>>   05:00.0 VGA compatible controller: NVIDIA Corporation GK208B [GeForce GT 720] (rev a1)
> In this example, all of the GPUs are driven by different drivers. What
> good does a module parameter do if you have multiple GPUs of the same
> model, all driven by the same driver module?

Completely agree. Question is what is the benefit for the end user to 
actually specify this?

If you want the initial console on a different device than implement a 
kernel options for vgaarb and *not* the drivers.

Regards,
Christian.

>
> BR,
> Jani.
>
>> $ sudo dmesg | grep vgaarb
>>
>>   pci 0000:00:02.0: vgaarb: setting as boot VGA device
>>   pci 0000:00:02.0: vgaarb: VGA device added: decodes=io+mem,owns=io+mem,locks=none
>>   pci 0000:01:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none
>>   pci 0000:04:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none
>>   pci 0000:05:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none
>>   vgaarb: loaded
>>   ast 0000:04:00.0: vgaarb: Override as primary by driver
>>   i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=none:owns=io+mem
>>   radeon 0000:01:00.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=none:owns=none
>>   ast 0000:04:00.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=none:owns=none
>>
>> v2:
>> 	* Add a simple implemment for drm/i915 and drm/ast
>> 	* Pick up all tags (Mario)
>> v3:
>> 	* Fix a mistake for drm/i915 implement
>> 	* Fix patch can not be applied problem because of merge conflect.
>> v4:
>> 	* Focus on solve the real problem.
>>
>> v1,v2 at https://patchwork.freedesktop.org/series/120059/
>>     v3 at https://patchwork.freedesktop.org/series/120562/
>>
>> [1] https://patchwork.freedesktop.org/series/122845/
>>
>> Sui Jingfeng (9):
>>    PCI/VGA: Allowing the user to select the primary video adapter at boot
>>      time
>>    drm/nouveau: Implement .be_primary() callback
>>    drm/radeon: Implement .be_primary() callback
>>    drm/amdgpu: Implement .be_primary() callback
>>    drm/i915: Implement .be_primary() callback
>>    drm/loongson: Implement .be_primary() callback
>>    drm/ast: Register as a VGA client by calling vga_client_register()
>>    drm/hibmc: Register as a VGA client by calling vga_client_register()
>>    drm/gma500: Register as a VGA client by calling vga_client_register()
>>
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c    | 11 +++-
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       | 13 ++++-
>>   drivers/gpu/drm/ast/ast_drv.c                 | 31 ++++++++++
>>   drivers/gpu/drm/gma500/psb_drv.c              | 57 ++++++++++++++++++-
>>   .../gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c   | 15 +++++
>>   drivers/gpu/drm/i915/display/intel_vga.c      | 15 ++++-
>>   drivers/gpu/drm/loongson/loongson_module.c    |  2 +-
>>   drivers/gpu/drm/loongson/loongson_module.h    |  1 +
>>   drivers/gpu/drm/loongson/lsdc_drv.c           | 10 +++-
>>   drivers/gpu/drm/nouveau/nouveau_vga.c         | 11 +++-
>>   drivers/gpu/drm/radeon/radeon_device.c        | 10 +++-
>>   drivers/pci/vgaarb.c                          | 43 ++++++++++++--
>>   drivers/vfio/pci/vfio_pci_core.c              |  2 +-
>>   include/linux/vgaarb.h                        |  8 ++-
>>   14 files changed, 210 insertions(+), 19 deletions(-)