From cf3d262e39941d8f148148e840c00fcbc35a8e6f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Fri, 14 Nov 2014 21:02:44 +0200 Subject: [PATCH] drm/i915: Fix comments about CHV snoop behaviour MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- drivers/gpu/drm/i915/i915_gem_gtt.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index 29a4486c62ad..2b008525bda2 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) |