From: Ville Syrjälä Date: Fri, 14 Nov 2014 19:02:44 +0000 (+0200) Subject: drm/i915: Fix comments about CHV snoop behaviour X-Git-Tag: v4.14-rc1~6290^2~14^2~60 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=cf3d262e39941d8f148148e840c00fcbc35a8e6f;p=platform%2Fkernel%2Flinux-rpi.git drm/i915: Fix comments about CHV snoop behaviour Replace the misinformed notes about CHV snoop behaviour with something that's hopefully closer to reality. Signed-off-by: Ville Syrjälä Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index 29a4486..2b00852 100644 --- a/drivers/gpu/drm/i915/i915_gem_gtt.c +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c @@ -1942,9 +1942,17 @@ static void chv_setup_private_ppat(struct drm_i915_private *dev_priv) * Only the snoop bit has meaning for CHV, the rest is * ignored. * - * Note that the harware enforces snooping for all page - * table accesses. The snoop bit is actually ignored for - * PDEs. + * The hardware will never snoop for certain types of accesses: + * - CPU GTT (GMADR->GGTT->no snoop->memory) + * - PPGTT page tables + * - some other special cycles + * + * As with BDW, we also need to consider the following for GT accesses: + * "For GGTT, there is NO pat_sel[2:0] from the entry, + * so RTL will always use the value corresponding to + * pat_sel = 000". + * Which means we must set the snoop bit in PAT entry 0 + * in order to keep the global status page working. */ pat = GEN8_PPAT(0, CHV_PPAT_SNOOP) | GEN8_PPAT(1, 0) |