Re: [PATCH 00/12] Recover sysfb after DRM probe failure

Christian König
2026-01-19T10:03:16Z

On 1/17/26 07:02, Zack Rusin wrote:
> On Fri, Jan 16, 2026 at 2:58 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>
>> Hi
>>
>> Am 16.01.26 um 04:59 schrieb Zack Rusin:
>>> On Thu, Jan 15, 2026 at 6:02 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>>> That's really not going to work. For example, in the current series, you
>>>> invoke devm_aperture_remove_conflicting_pci_devices_done() after
>>>> drm_mode_reset(), drm_dev_register() and drm_client_setup().
>>> That's perfectly fine,
>>> devm_aperture_remove_conflicting_pci_devices_done is removing the
>>> reload behavior not doing anything.
>>>
>>> This series, essentially, just adds a "defer" statement to
>>> aperture_remove_conflicting_pci_devices that says
>>>
>>> "reload sysfb if this driver unloads".
>>>
>>> devm_aperture_remove_conflicting_pci_devices_done just cancels that defer.
>>
>> Exactly. And if that reload happens after the hardware state has been
>> changed, the result is undefined.
>
> This is all predicated on drivers actually cleaning up after
> themselves. I don't think any amount of good will or api design is
> going to fix device specific state mismatches.
>
>> The current recovery/reload is not reliable in any case. A number of
>> high-profile devs have also said that it doesn't work with their driver.
>> The same is true for ast. So the current approach is not going to happen.
>>
>>> There also might be the case of some crazy behavior, e.g. pci bar
>>> resize in the driver makes the vga hardware crash or something, in
>>> which case, yea, we should definitely skip this patch, at least until
>>> those drivers properly cleanup on exit.
>>
>> There's nothing crazy here. It's standard probing code.
>>
>> If you want to to move forward, my suggestion is to look at the proposal
>> with the aperture_funcs callbacks that control sysfb device access. And
>> from there, build a full prototype with one or two drivers.
>
> I don't think that approach is going to work. I don't think there's
> anything that can be done if drivers didn't cleanup everything they've
> done that might have broken sysfb on unload. I'm going to drop it
> then, it's obviously a shame because it works fine with virtualized
> drivers and they're ones that would likely profit from this the most
> but I'm sceptical that I could do full system state set reset in a
> generalized fashion for hw drivers or that the work required would be
> worth the payoff.

Well at least for PCI devices you could try doing a function level reset to get the HW back into some usable state.

This does *not* work for AMD HW since we have HW/FW bugs, but at least for your virtualized use case it might work.

All you need then is an EFI, Vesa or int10 call to re-init the HW to the pre-driver load setup.

I know that is not the easiest thing to do, but still better than a black screen.

Regards,
Christian.

>
> z