[Intel-gfx] Enabling i915.fastboot=1 by default

[Hans de Goede]

Hi,

On 06-06-18 11:36, Maarten Lankhorst wrote:
> Op 06-06-18 om 11:09 schreef Hans de Goede:
>> Hi All,
>>
>> So I'm working on making Linux boot in a complete
>> flickerfree manner (no modesets, no black screens).
>>
>> I have this working on various machines with Intel
>> gfx, but I need to pass i915.fastboot=1 on the kernel
>> commandline.
>>
>> I know there was some talk about enabling this by
>> default a while ago, but it seems that that still
>> has not happened (yet?).
>>
>> I'm wondering what is holding this back ? Maybe we
>> can change it from a bool to an int, init it to -1
>> and when it is -1 have some automatic detection
>> code which disables it where it is known to be
>> troublesome and otherwise enables it by default?
> 
> Main reason are bugs like https://bugs.freedesktop.org/show_bug.cgi?id=103781 and our hw
> readout not being perfect. On some haswell/broadwell eDP laptops we stop generating vblanks
> when we fastboot, and in general we don't trust our code enough for that.
> 
> The automatic detection code is already in place, we modeset if the mode is not compatible
> enough, but we don't catch all the cases where this might happen.

Right but the "mode is not compatible" check will be always
necessary, because e.g. some BIOs-es insist in bringing
up the display in 1024x768 instead of its native mode.

What I meant is, something like check which generation we are on
(and maybe if a specific type of output is used or not if that
does not convolute the code too much).

E.g. you mention vblank issues with haswell/broadwell eDP,
so if i915.fastboot=-1 we would then disable fastboot
if we are on a haswell or broadwell and eDP is used.

Or we could simply disable it on all haswell/broadwell devices
when i915.fastboot=-1 used, but maybe enable on skylake and
newer?

Regards,

Hans