[Saucy][SRU][PATCH 1/1] (no-up) Revert "Revert "drm/i915: revert eDP bpp clamping code changes""

[Joseph Salisbury]

On 10/16/2013 04:57 PM, Joseph Salisbury wrote:
> BugLink: http://bugs.launchpad.net/bugs/1195483
>
> This reverts commit 657445fe8660100ad174600ebfa61536392b7624.
>
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 26e162b..ce933ad 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -709,10 +709,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  
>  	/* Walk through all bpp values. Luckily they're all nicely spaced with 2
>  	 * bpc in between. */
> -	bpp = pipe_config->pipe_bpp;
> -	if (is_edp(intel_dp) && dev_priv->vbt.edp_bpp)
> -		bpp = min_t(int, bpp, dev_priv->vbt.edp_bpp);
> -
> +	bpp = min_t(int, 8*3, pipe_config->pipe_bpp);
>  	for (; bpp >= 6*3; bpp -= 2*3) {
>  		mode_rate = intel_dp_link_required(adjusted_mode->clock, bpp);
>  
> @@ -763,6 +760,19 @@ found:
>  			       &pipe_config->dp_m_n);
>  
>  	intel_dp_set_clock(encoder, pipe_config, intel_dp->link_bw);
> +	/*
> +	 * XXX: We have a strange regression where using the vbt edp bpp value
> +	 * for the link bw computation results in black screens, the panel only
> +	 * works when we do the computation at the usual 24bpp (but still
> +	 * requires us to use 18bpp). Until that's fully debugged, stay
> +	 * bug-for-bug compatible with the old code.
> +	 */
> +	if (is_edp(intel_dp) && dev_priv->vbt.edp_bpp) {
> +		DRM_DEBUG_KMS("clamping display bpc (was %d) to eDP (%d)\n",
> +			      bpp, dev_priv->vbt.edp_bpp);
> +		bpp = min_t(int, bpp, dev_priv->vbt.edp_bpp);
> +	}
> +	pipe_config->pipe_bpp = bpp;
>  
>  	return true;
>  }

A proper fix is also being discussed upstream:
https://bugzilla.kernel.org/show_bug.cgi?id=59841

Maybe an alternative to this patch is to add something to the Saucy
release notes until this is fixed upstream?