[PATCH] [Quantal](pre-stable)drm/i915/lvds: ditch ->prepare special case

[Colin Ian King]

On 24/01/13 08:46, Haitao Zhang wrote:
>  From 3273adbb6123abdda68695b663b1c4cc97e00fe9 Mon Sep 17 00:00:00 2001
> From: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date: Wed, 11 Jul 2012 16:27:52 +0200
> Subject: [PATCH] [Quantal](pre-stable)drm/i915/lvds: ditch ->prepare special
>   case
>
> LVDS is the first output where dpms on/off and prepare/commit don't
> perfectly match. Now the idea behind this special case seems to be
> that for simple resolution changes on the LVDS we don't need to stop
> the pipe, because (at least on newer chips) we can adjust the panel
> fitter on the fly.
>
> There are a few problems with the current code though:
> - We still stop and restart the pipe unconditionally, because the crtc
>    helper code isn't flexible enough.
> - We show some ugly flickering, especially when changing crtcs (this
>    the crtc helper would actually take into account, but we don't
>    implement the encoder->get_crtc callback required to make this work
>    properly).
>
> So it doesn't even work as advertised. I agree that it would be nice
> to do resolution changes on LVDS (and also eDP) whithout blacking the
> screen where the panel fitter allows to do that. But imo we should
> implement this as a special case a few layers up in the mode set code,
> akin to how we already detect simple framebuffer changes (and only
> update the required registers with ->mode_set_base).
>
> Until this is all in place, make our lives easier and just rip it out.
>
> Also note that this seems to fix actual bugs with enabling the lvds
> output, see:
>
> http://lists.freedesktop.org/archives/intel-gfx/2012-July/018614.html
>
> Cc: Takashi Iwai <tiwai at suse.de>
> Cc: Giacomo Comes <comes at naic.edu>
> Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
> Tested-by: Takashi Iwai <tiwai at suse.de>
> Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> (Cherry-picked from commit 520c41cf2fa029d1e8b923ac2026f96664f17c4b)
> BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1103856
> Signed-Off-by: Haitao Zhang <haitao.zhang at canonical.com>
> ---
>   drivers/gpu/drm/i915/intel_lvds.c |    8 +-------
>   1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
> index f85e2b1..3aa53e9 100644
> --- a/drivers/gpu/drm/i915/intel_lvds.c
> +++ b/drivers/gpu/drm/i915/intel_lvds.c
> @@ -408,13 +408,7 @@ static void intel_lvds_prepare(struct drm_encoder *encoder)
>   {
>   	struct intel_lvds *intel_lvds = to_intel_lvds(encoder);
>
> -	/*
> -	 * Prior to Ironlake, we must disable the pipe if we want to adjust
> -	 * the panel fitter. However at all other times we can just reset
> -	 * the registers regardless.
> -	 */
> -	if (!HAS_PCH_SPLIT(encoder->dev) && intel_lvds->pfit_dirty)
> -		intel_lvds_disable(intel_lvds);
> +	intel_lvds_disable(intel_lvds);
>   }
>
>   static void intel_lvds_commit(struct drm_encoder *encoder)
>

Well, this seems to be accepted upstream.  It also seems to fix other 
bugs when enabling LVS as referenced in the freedesktop link.  My only 
real concern is possible regressions on chipsets other than the one 
tested.  What kind of testing has been run on this fix?

Colin