[PATCH 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 and use more local variables for clearer
   logic (Ursulin)
v7:
 - Rebased.
v8:
 - Reviewed by Oscar.
v9:
 - Fixed label location. (Oscar)
v10:
 - Improved comments and replaced magical number. (Oscar)

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>
Reviewed-by: Oscar Mateo <oscar.mateo at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h          |  4 ++++
 drivers/gpu/drm/i915/intel_device_info.c | 34 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index fb10602..6c9c01b 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2709,6 +2709,10 @@ 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_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
index d917c9b..44ca90a 100644
--- a/drivers/gpu/drm/i915/intel_device_info.c
+++ b/drivers/gpu/drm/i915/intel_device_info.c
@@ -729,6 +729,40 @@ static void sanitize_mcr(struct intel_device_info *info)
 	u32 slice = fls(info->sseu.slice_mask);
 	u32 subslice = fls(info->sseu.subslice_mask[slice]);
 
+	/*
+	 * WaProgramMgsrForL3BankSpecificMmioReads: cnl,icl
+	 * L3Banks could be fused off in single slice scenario. If that is
+	 * the case, we might need to program MCR select to a valid L3Bank
+	 * by default, to make sure we correctly read certain registers
+	 * later on (in the range 0xB100 - 0xB3FF).
+	 * This might be incompatible with
+	 * WaProgramMgsrForCorrectSliceSpecificMmioReads.
+	 * Fortunately, this should not happen in production hardware, so
+	 * we only assert that this is the case (instead of implementing
+	 * something more complex that requires checking the range of every
+	 * MMIO read).
+	 */
+	if (INTEL_GEN(dev_priv) >= 10 &&
+	    is_power_of_2(info->sseu.slice_mask)) {
+		/*
+		 * read FUSE3 for enabled L3 Bank IDs, if L3 Bank matches
+		 * enabled subslice, no need to redirect MCR packet
+		 */
+		u32 fuse3 = I915_READ(GEN10_MIRROR_FUSE3);
+		u8 ss_mask = info->sseu.subslice_mask[slice];
+
+		u8 enabled_mask = (ss_mask | ss_mask >>
+				   GEN10_L3BANK_PAIR_COUNT) &
+				   GEN10_L3BANK_MASK;
+		u8 disabled_mask = fuse3 & GEN10_L3BANK_MASK;
+
+		/*
+		 * Production silicon should have matched L3Bank and
+		 * subslice enabled
+		 */
+		WARN_ON((enabled_mask & disabled_mask) != enabled_mask);
+	}
+
 	if (INTEL_GEN(dev_priv) >= 11) {
 		mcr_slice_subslice_mask = GEN11_MCR_SLICE_MASK |
 					  GEN11_MCR_SUBSLICE_MASK;
-- 
2.7.4