[Intel-gfx] [PATCH] drm/i915: Treat resetting of the current framebuffer as a no-op

[Paulo Zanoni]

2013/5/31 Daniel Vetter <daniel at ffwll.ch>:
> On Fri, May 31, 2013 at 4:05 PM, Paulo Zanoni <przanoni at gmail.com> wrote:
>> 2013/5/23 Daniel Vetter <daniel at ffwll.ch>:
>>> On Thu, May 23, 2013 at 01:57:17PM +0100, Chris Wilson wrote:
>>>> If none of the CRTC parameters change along with the framebuffer, we can
>>>> forgo rewriting the register and waiting for a vblank. There are a few
>>>> calls made by the display managers as they start up which tend to end up
>>>> performing no-ops on the current CRTC settings.
>>>>
>>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>
>>> Makes sense. Queued for -next, thanks for the patch. Now the only things
>>> left (besides beating fastboot into good shape) is to cache the edids a
>>> bit and we've (hopefully) killed all kms stalls at startup ...
>>
>> This commit introduced a regression.
>>
>> - Boot with both eDP and DP plugged
>> - When I boot like this, eDP1 has 1920x1080 and DP1 has 1920x1080i.
>> - Run "xrandr --output DP1 --mode 0x55" (that's 1024x768 at 60Hz here)
>> - See the black screen on DP output, dmesg has the "skipping reset of
>> current fb" message.
>> - After we get the black screen, if we run "xrandr --output DP1 --off;
>> xrandr --output DP1 --mode 0x55" the mode will work.
>>
>> If I diff the "bad state" with the "good state" we'll see the cause is
>> the DSPCNTR register. When we do the early return in
>> intel_pipe_set_base we don't call the update_plane function. For me
>> what changes is the pixel format and the trickle feed bits.
>
> Oh, in the modeset case we can't optimize the update_fb away, even
> when both fbs are the same ...
>
> Just to check that our level of paranoia is still high enough: Has the
> modeset state checker complained or not?

No. The register diff is really only a few bits of the DSPCNTR register.


> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
Paulo Zanoni