Re: [PATCH] drm/i915: properly compute dp dithering for user-created modes

[Chris Wilson <chris@chris-wilson.co.uk>]

On Tue, 10 Apr 2012 09:33:19 +0200, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> We've only computed whether we need to fall back to 6bpc due to dp
> link bandwidth constrains in mode_valid, but not mode_fixup. Under
> various circumstances X likes to create new modes which then lack
> proper 6bpc flags (if required), resulting in mode_fixup failures and
> ultimately black screens.
> 
> This is hopefully fixes the last regression fallout of the dp
> bandwidth fixes.

Based on my reading, this still leaves the issue of depth > 24 modes as
the upper bandwidth required is calculated on the presumption of
depth == 24, but the divider set to the fb depth in the normal case.
 
> The likely culprit for this regression is
> 
> commit 3d794f87238f74d80e78a7611c7fbde8a54c85c2
> Author: Keith Packard <keithp@keithp.com>
> Date:   Wed Jan 25 08:16:25 2012 -0800
> 
>     drm/i915: Force explicit bpp selection for intel_dp_link_required
> 
> Reported-and-tested-by: Brice Goglin <Brice.Goglin@ens-lyon.org>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=48170
> Cc: stable@kernel.org
> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   49 +++++++++++++++++++++++++++-----------
>  1 files changed, 35 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 110552f..065c26d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -219,14 +219,38 @@ intel_dp_max_data_rate(int max_link_clock, int max_lanes)
>  	return (max_link_clock * max_lanes * 8) / 10;
>  }
>  
> +static bool
> +intel_dp_adjust_dithering(struct intel_dp *intel_dp,
> +			  struct drm_display_mode *mode,
> +			  struct drm_display_mode *adjusted_mode)
> +{
> +	int max_link_clock = intel_dp_link_clock(intel_dp_max_link_bw(intel_dp));
> +	int max_lanes = intel_dp_max_lane_count(intel_dp);
> +	int max_rate, mode_rate;
> +
> +	mode_rate = intel_dp_link_required(mode->clock, 24);
> +	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
> +
> +	if (mode_rate > max_rate) {
> +			mode_rate = intel_dp_link_required(mode->clock, 18);
Cut'n'paste bad whitespace.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre