[Intel-gfx] [PATCH] drm/i915: Disable LVDS while modesetting for HD+ panels

[Daniel Vetter]

On Mon, Jul 02, 2012 at 06:14:54PM +0200, Takashi Iwai wrote:
> Some SNB/IVY Laptops with 1600x900 HD+ panel (e.g. Dell Latitude E6420
> and HP ProBook 65xx) are known to show the whole black/white garbage
> or flickering screens while starting up or changing the mode.
> This can be worked around by disabling LVDS off while changing the
> mode.
> 
> Since this doesn't give any visible drawback on machines I've tested,
> enable it generically for HD+ panels for SCH-split case.
> 
> Tested-by: Giacomo Comes <comes at naic.edu>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>

As part of a larger rework effort for the modeset stuff I've stumbled over
this, too - I see detiled garbage on some mode switches.

http://cgit.freedesktop.org/~danvet/drm/commit/?h=modeset-rework&id=bf8528171b2c2bb94aeca8316e26e017e42643d3

So my question: why so complicated, and what's the justification for the
funky hdisplay/vdisplay condiditons?

Cheers, Daniel

> ---
>  drivers/gpu/drm/i915/intel_lvds.c |   25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
> index 08eb04c..cf1c150 100644
> --- a/drivers/gpu/drm/i915/intel_lvds.c
> +++ b/drivers/gpu/drm/i915/intel_lvds.c
> @@ -407,13 +407,26 @@ out:
>  static void intel_lvds_prepare(struct drm_encoder *encoder)
>  {
>  	struct intel_lvds *intel_lvds = to_intel_lvds(encoder);
> +	bool do_disable = false;
>  
> -	/*
> -	 * 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)
> +	if (HAS_PCH_SPLIT(encoder->dev)) {
> +		/* Some HD+ panels require the pipe-off while mode changing;
> +		 * otherwise you'll get B/W garbage or sustaining flickering
> +		 * screen
> +		 */
> +		if (intel_lvds->fixed_mode->hdisplay >= 1600 &&
> +		    intel_lvds->fixed_mode->vdisplay >= 900)
> +			do_disable = true;
> +	} else {
> +		/*
> +		 * 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.
> +		 */
> +		do_disable = intel_lvds->pfit_dirty;
> +	}
> +
> +	if (do_disable)
>  		intel_lvds_disable(intel_lvds);
>  }
>  
> -- 
> 1.7.10.4
> 
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-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48