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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]



Am 05.09.23 um 17:59 schrieb suijingfeng:
FYI: per-driver modeset parameters are deprecated and not to be used. Please don't promote them.

Well, please wait, I want to explain.

drm/nouveau already promote it a little bit.

Despite no code of conduct or specification guiding how the modules parameters should be. Noticed that there already have a lot of DRM drivers support the modeset parameters,

Please look at the history and discussion around this parameter. To my knowledge, 'modeset' got introduced when modesetting with still done in userspace. It was an easy way of disabling the kernel driver if the system's Xorg did no yet support kernel mode setting.

Fast forward a few years and all Linux' use kernel modesetting, which make the modeset parameters obsolete. We discussed and decided to keep them in, because many articles and blog posts refer to them. We didn't want to invalidate them. BUT modeset is deprecated and not allowed in new code. If you look at existing modeset usage, you will eventually come across the comment at [1].

There's 'nomodeset', which disables all native drivers. It's useful for debugging or as a quick-fix if the graphics driver breaks. If you want to disable a specific driver, please use one of the options for blacklisting.

Best regards


for the modeset parameter, authors of various device driver try to make the usage not
conflict with others. I believe that this is good thing for Linux users.
It is probably the responsibility of the drm core maintainers to force various drm drivers to reach a minimal consensus. Probably it pains to do so and doesn't pay off.
But reach a minimal consensus do benefit to Linux users.

You can use modprobe.blacklist or initcall_blacklist on the kernel command line.

There are some cases where the modprobe.blacklist doesn't works,
I have come cross several time during the past.
Because the device selected by the VGAARB is device-level thing,
it is not the driver's problem.

Sometimes when VGAARB has a bug, it will select a wrong device as primary.
And the X server will use this wrong device as primary and completely crash
there, due to lack a driver. Take my old S3 Graphics as an example:

$ lspci | grep VGA

 00:06.1 VGA compatible controller: Loongson Technology LLC DC (Display Controller) (rev 01)  03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos XT [Radeon HD 7470/8470 / R5 235/310 OEM]
  07:00.0 VGA compatible controller: S3 Graphics Ltd. Device 9070 (rev 01)
  08:00.0 VGA compatible controller: S3 Graphics Ltd. Device 9070 (rev 01)

Before apply this patch:

[    0.361748] pci 0000:00:06.1: vgaarb: setting as boot VGA device
[    0.361753] pci 0000:00:06.1: vgaarb: VGA device added: decodes=io+mem,owns=io+mem,locks=none [    0.361765] pci 0000:03:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none [    0.361773] pci 0000:07:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none [    0.361779] pci 0000:08:00.0: vgaarb: VGA device added: decodes=io+mem,owns=none,locks=none
[    0.361781] vgaarb: loaded
[    0.367838] pci 0000:00:06.1: Overriding boot device as 1002:6778
[    0.367841] pci 0000:00:06.1: Overriding boot device as 5333:9070
[    0.367843] pci 0000:00:06.1: Overriding boot device as 5333:9070

For known reason, one of my system select the S3 Graphics as primary GPU.
But this S3 Graphics not even have a decent drm upstream driver yet.
Under such a case, I begin to believe that only the device who has a
driver deserve the primary.

Under such a condition, I want to reboot and enter the graphic environment
with other working video cards. Either platform integrated and discrete GPU.
This don't means I should compromise by un-mount the S3 graphics card from
the motherboard, this also don't means that I should update my BIOS setting.
As sometimes, the BIOS is more worse.

With this series applied, all I need to do is to reboot the computer and
pass a command line. By force override another video card (who has a
decent driver support) as primary, I'm able to do the debugging under
graphic environment. I would like to examine what's wrong with the vgaarb
on a specific platform under X server graphic environment.

Probably try compile a driver for this card and see it works, simply reboot
without the need to change anything. It is so efficient. So this is probably
the second usage of my patch. It hand the right of control back to the
graphic developer.

Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Attachment: OpenPGP_signature
Description: OpenPGP digital signature

[Index of Archives]     [DMA Engine]     [Linux Coverity]     [Linux USB]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Greybus]

  Powered by Linux