From 16af25faae8ef72b4ff2feeca65f6e864c3ef929 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Fri, 19 Jan 2018 16:41:52 +0200 Subject: [PATCH] drm/i915: Add a comment exlaining CCS hsub/vsub MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Let's document why we claim hsub==8,vsub==16 for CCS. v2: Replace my explanation with Jason's Cc: Daniel Vetter Cc: Ben Widawsky Cc: Jason Ekstrand Cc: Daniel Stone Signed-off-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20180119144152.17224-1-ville.syrjala@linux.intel.com Reviewed-by: Jason Ekstrand --- drivers/gpu/drm/i915/intel_display.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 03b817279a5b..f9372a21e326 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -2387,6 +2387,20 @@ static unsigned int intel_fb_modifier_to_tiling(uint64_t fb_modifier) } } +/* + * From the Sky Lake PRM: + * "The Color Control Surface (CCS) contains the compression status of + * the cache-line pairs. The compression state of the cache-line pair + * is specified by 2 bits in the CCS. Each CCS cache-line represents + * an area on the main surface of 16 x16 sets of 128 byte Y-tiled + * cache-line-pairs. CCS is always Y tiled." + * + * Since cache line pairs refers to horizontally adjacent cache lines, + * each cache line in the CCS corresponds to an area of 32x16 cache + * lines on the main surface. Since each pixel is 4 bytes, this gives + * us a ratio of one byte in the CCS for each 8x16 pixels in the + * main surface. + */ static const struct drm_format_info ccs_formats[] = { { .format = DRM_FORMAT_XRGB8888, .depth = 24, .num_planes = 2, .cpp = { 4, 1, }, .hsub = 8, .vsub = 16, }, { .format = DRM_FORMAT_XBGR8888, .depth = 24, .num_planes = 2, .cpp = { 4, 1, }, .hsub = 8, .vsub = 16, }, -- 2.30.2