[Intel-gfx] [PATCH v6 2/2] drm/i915: Implement WaProgramMgsrForL3BankSpecificMmioReads

[Yunwei Zhang]

L3Bank could be fused off in hardware for debug purpose, and it
is possible that subslice is enabled while its corresponding L3Bank pairs
are disabled. In such case, if MCR packet control register(0xFDC) is
programed to point to a disabled bank pair, a MMIO read into L3Bank range
will return 0 instead of correct values.

However, this is not going to be the case in any production silicon.
Therefore, we only check at initialization and issue a warning should
this really happen.

References: HSDES#1405586840

v2:
 - use fls instead of find_last_bit (Chris)
 - use is_power_of_2() instead of counting bit set (Chris)
v3:
 - rebase on latest tip
v5:
 - Added references (Mika)
 - Move local variable into scope where they are used (Ursulin)
 - use a new local variable to reduce long line of code (Ursulin)
v6:
 - Some coding style change and uses of local variables for clearer
   logic (Ursulin)

Cc: Oscar Mateo <oscar.mateo at intel.com>
Cc: Michel Thierry <michel.thierry at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Signed-off-by: Yunwei Zhang <yunwei.zhang at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h        |  4 ++++
 drivers/gpu/drm/i915/intel_engine_cs.c | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 32c297a..994870f 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2697,6 +2697,10 @@ enum i915_power_well_id {
 #define   GEN10_F2_SS_DIS_SHIFT		18
 #define   GEN10_F2_SS_DIS_MASK		(0xf << GEN10_F2_SS_DIS_SHIFT)
 
+#define	GEN10_MIRROR_FUSE3		_MMIO(0x9118)
+#define GEN10_L3BANK_PAIR_COUNT     4
+#define GEN10_L3BANK_MASK   0x0F
+
 #define GEN8_EU_DISABLE0		_MMIO(0x9134)
 #define   GEN8_EU_DIS0_S0_MASK		0xffffff
 #define   GEN8_EU_DIS0_S1_SHIFT		24
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 4c50bee..57f4c35 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -810,8 +810,33 @@ static u32 calculate_mcr(struct drm_i915_private *dev_priv, u32 mcr)
 
 static void wa_init_mcr(struct drm_i915_private *dev_priv)
 {
+	const struct sseu_dev_info *sseu = &(INTEL_INFO(dev_priv)->sseu);
 	u32 mcr;
 
+	/*
+	 * L3Banks could be fused off in single slice scenario, however, if
+	 * more than one slice is enabled, this should not happen.
+	 */
+	if (is_power_of_2(sseu->slice_mask)) {
+		/*
+		 * WaProgramMgsrForL3BankSpecificMmioReads:
+		 * read FUSE3 for enabled L3 Bank IDs, if L3 Bank matches
+		 * enabled subslice, no need to redirect MCR packet
+		 */
+		u32 slice = fls(sseu->slice_mask);
+		u32 fuse3 = I915_READ(GEN10_MIRROR_FUSE3);
+		u8 ss_mask = sseu->subslice_mask[slice];
+
+		u8 enabled_mask = (ss_mask | ss_mask >> 4) & 0xf;
+		u8 disabled_mask = fuse3 & 0xf;
+
+		/*
+		 * Production silicon should have matched L3Bank and
+		 * subslice enabled
+		 */
+		WARN_ON((enabled_mask & disabled_mask) != enabled_mask);
+	}
+
 	mcr = I915_READ(GEN8_MCR_SELECTOR);
 	mcr = calculate_mcr(dev_priv, mcr);
 	I915_WRITE(GEN8_MCR_SELECTOR, mcr);
-- 
2.7.4