linux-kernel - Re: [Intel-gfx] [PATCH 4/7] drm/i915: Check display_bpc against max_fdi_bpp after display

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Date:	Fri, 17 Aug 2012 15:58:57 +0100
From:	"Lespiau, Damien" <damien.lespiau@...el.com>
To:	Keith Packard <keithp@...thp.com>
Cc:	intel-gfx@...ts.freedesktop.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 4/7] drm/i915: Check display_bpc against
 max_fdi_bpp after display_bpc is set

On Tue, Aug 14, 2012 at 5:34 AM, Keith Packard <keithp@...thp.com> wrote:
> @@ -3845,8 +3836,20 @@ static bool intel_choose_pipe_bpp_dither(struct drm_crtc *crtc,
>
>         display_bpc = min(display_bpc, bpc);
>
> -       DRM_DEBUG_KMS("setting pipe bpc to %d (max display bpc %d)\n",
> -                     bpc, display_bpc);
> +       display_bpc = 6;

It seems that you are overriding display_bpc unconditionally here,
some left over from debugging?

> +       if (display_bpc * 3 > max_fdi_bpp) {
> +               if (max_fdi_bpp < 24)
> +                       display_bpc = 6;
> +               else if (max_fdi_bpp < 30)
> +                       display_bpc = 8;
> +               else if (max_fdi_bpp < 36)
> +                       display_bpc = 10;
> +               DRM_DEBUG_KMS("Dithering FDI to %dbpc\n", display_bpc);
> +       }
> +
> +       DRM_DEBUG_KMS("setting pipe bpc to %d (max display bpc %d) (max_fdi_bpp %d)\n",
> +                     bpc, display_bpc, max_fdi_bpp);
>
>         *pipe_bpp = display_bpc * 3;

"setting pipe bpc to %d", bpc and  *pipe_bpp = display_bpc, looks like
a bogus debug message to me.

> @@ -4763,9 +4765,12 @@ static int ironlake_crtc_mode_set(struct drm_crtc *crtc,
>                  * Compute the available FDI bandwidth, use that
>                  * to compute the maximum supported BPP
>                  */
> -               fdi_bw = link_bw * max_lane * 19 / 20;
> -               max_fdi_bpp = fdi_bw / target_clock;
> -               DRM_DEBUG_KMS("max lane %d yields max fdi bpp %d\n", max_lane, max_fdi_bpp);
> +               fdi_bw = (link_bw * 8) * max_lane;
> +               pps = target_clock * 21 / 20;
> +
> +               max_fdi_bpp = fdi_bw / pps;
> +               DRM_DEBUG_KMS("link_bw %d max_lane %d fdi_bw %u pps %u max_fdi_bpp %d\n",
> +                             link_bw, max_lane, fdi_bw, pps, max_fdi_bpp);
>         }

While I understood the first computation of max_fdi_bpp in patch 2 of
this series, I have to confess you lost me there. Would you mind
clarifying this?

-- 
Damien
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