[Intel-gfx] [PATCH] drm/i915: no longer call drm_helper_resume_force_mode

[Daniel Vetter]

On Wed, Sep 5, 2012 at 8:31 PM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> On Wed, 29 Aug 2012 23:13:29 +0200
> Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
>> Since this only calls crtc helper functions, of which a shocking
>> amount are NULL.
>>
>> Now the curious thing is how the new modeset code worked with this
>> function call still present:
>>
>> Thanks to the hw state readout and the suspend fixes to properly
>> quiescent the register state, nothing is actually enabled at resume
>> (if the bios doesn't set up anything). Which means resume_force_mode
>> doesn't actually do anything and hence nothing blows up at resume
>> time.
>>
>> The other reason things do work is that the fbcon layer has it's own
>> resume notifier callback, which restores the mode. And thanks to the
>> force vt switch at suspend/resume, that then forces X to restore it's
>> own mode.
>>
>> Hence everything still worked (as long as the bios doesn't enable
>> anything). And we can just kill the call to resume_force_mode.
>>
>> The upside of both this patch and the preceeding patch to quiescent
>> the modeset state is that our resume path is much simpler:
>> - We now longer restore bogus register values (which most often would
>>   enable the backlight a bit and a few ports), causing flickering.
>> - We now longer call resume_force_mode to restore a mode that the
>>   fbcon layer would overwrite right away anyway.
>>
>> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>> ---
>>  drivers/gpu/drm/i915/i915_drv.c | 5 -----
>>  1 file changed, 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
>> index fe7512a..cd6697c 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.c
>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>> @@ -549,11 +549,6 @@ static int i915_drm_thaw(struct drm_device *dev)
>>               intel_modeset_setup_hw_state(dev);
>>               drm_mode_config_reset(dev);
>>               drm_irq_install(dev);
>> -
>> -             /* Resume the modeset for every activated CRTC */
>> -             mutex_lock(&dev->mode_config.mutex);
>> -             drm_helper_resume_force_mode(dev);
>> -             mutex_unlock(&dev->mode_config.mutex);
>>       }
>>
>>       intel_opregion_init(dev);
>
> Wouldn't the fb layer's modeset end up being a no-op if the suspended
> mode was the same as the fb mode (often the case)?  Or at the very
> least just a flip rather than a full mode set.

I guess most of the flicker was because the register restoring
restored a bunch of crap (since the old modeset state wasn't properly
cleared before suspending).

> Though we do need to deal with non-fb, non-X resumes as well.  kmscon
> and wayland will expect to be restored at resume time even if CONFIG_VT
> and the fb layer aren't compiled into the kernel.

Tbh I was rather surprised that when I've noticed this little issue
here the restore still worked - until I've noticed by looking at the
logs that both the fbcon and the X server restore their modes.

I'm not sure what exactly we should do here, since even with the
current code the concept of a controlling node isn't really defined in
the kms interface (fbcon uses a bunch of funky checks to ensure it
doesn't clobber the output state of someone else). But for now (with
fbcon pretty much being non-optional) things keep on working, and
afaict actually work a bit better overall.
-Daniel
-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch