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

[Daniel Vetter]

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