drm/i915: Add support for explicit L3BANK steering

Because Render Power Gating restricts us to just a single subslice as a
valid steering target for reads of multicast registers in a SUBSLICE
range, the default steering we setup at init may not lead to a suitable
target for L3BANK multicast register.  In cases where it does not, use
explicit runtime steering whenever an L3BANK multicast register is read.

While we're at it, let's simplify the function a little bit and drop its
support for gen10/CNL since no such platforms ever materialized for real
use.  Multicast register steering is already an area that causes enough
confusion; no need to complicate it with what's effectively dead code.

v2:
 - Use gt->uncore instead of gt->i915->uncore.  (Tvrtko)
 - Use {} as table terminator.  (Rodrigo)

v3:
 - L3bank fuse register is a disable mask rather than an enable mask.
   We need to invert it before use.  (CI)

v4:
 - L3bank ID goes in the subslice field, not the slice field.  (CI)

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210617211425.1943662-4-matthew.d.roper@intel.com

drivers/gpu/drm/i915/gt/intel_gt.c

@@ -84,6 +84,11 @@ void intel_gt_init_hw_early(struct intel_gt *gt, struct i915_ggtt *ggtt)
 	gt->ggtt = ggtt;
 }
 
+static const struct intel_mmio_range icl_l3bank_steering_table[] = {
+	{ 0x00B100, 0x00B3FF },
+	{},
+};
+
 int intel_gt_init_mmio(struct intel_gt *gt)
 {
 	intel_gt_init_clock_frequency(gt);
@@ -91,6 +96,13 @@ int intel_gt_init_mmio(struct intel_gt *gt)
 	intel_uc_init_mmio(&gt->uc);
 	intel_sseu_info_init(gt);
 
+	if (GRAPHICS_VER(gt->i915) >= 11) {
+		gt->steering_table[L3BANK] = icl_l3bank_steering_table;
+		gt->info.l3bank_mask =
+			~intel_uncore_read(gt->uncore, GEN10_MIRROR_FUSE3) &
+			GEN10_L3BANK_MASK;
+	}
+
 	return intel_engines_init_mmio(gt);
 }
 
@@ -748,6 +760,12 @@ static void intel_gt_get_valid_steering(struct intel_gt *gt,
 					u8 *sliceid, u8 *subsliceid)
 {
 	switch (type) {
+	case L3BANK:
+		GEM_DEBUG_WARN_ON(!gt->info.l3bank_mask); /* should be impossible! */
+
+		*sliceid = 0;		/* unused */
+		*subsliceid = __ffs(gt->info.l3bank_mask);
+		break;
 	default:
 		MISSING_CASE(type);
 		*sliceid = 0;

drivers/gpu/drm/i915/gt/intel_gt_types.h

@@ -49,6 +49,8 @@ struct intel_mmio_range {
  * need to explicitly re-steer reads of registers of the other type.
  */
 enum intel_steering_type {
+	L3BANK,
+
 	NUM_STEERING_TYPES
 };
 
@@ -177,6 +179,8 @@ struct intel_gt {
 		/* Media engine access to SFC per instance */
 		u8 vdbox_sfc_access;
 
+		u32 l3bank_mask;
+
 		/* Slice/subslice/EU info */
 		struct sseu_dev_info sseu;
 	} info;

drivers/gpu/drm/i915/gt/intel_workarounds.c

@@ -945,71 +945,37 @@ cfl_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
 }
 
 static void
-wa_init_mcr(struct drm_i915_private *i915, struct i915_wa_list *wal)
+icl_wa_init_mcr(struct drm_i915_private *i915, struct i915_wa_list *wal)
 {
 	const struct sseu_dev_info *sseu = &i915->gt.info.sseu;
 	unsigned int slice, subslice;
-	u32 l3_en, mcr, mcr_mask;
+	u32 mcr, mcr_mask;
 
-	GEM_BUG_ON(GRAPHICS_VER(i915) < 10);
+	GEM_BUG_ON(GRAPHICS_VER(i915) < 11);
+	GEM_BUG_ON(hweight8(sseu->slice_mask) > 1);
+	slice = 0;
 
 	/*
-	 * 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).
-	 *
-	 * WaProgramMgsrForCorrectSliceSpecificMmioReads:cnl,icl
-	 * Before any MMIO read into slice/subslice specific registers, MCR
-	 * packet control register needs to be programmed to point to any
-	 * enabled s/ss pair. Otherwise, incorrect values will be returned.
-	 * This means each subsequent MMIO read will be forwarded to an
-	 * specific s/ss combination, but this is OK since these registers
-	 * are consistent across s/ss in almost all cases. In the rare
-	 * occasions, such as INSTDONE, where this value is dependent
-	 * on s/ss combo, the read should be done with read_subslice_reg.
-	 *
-	 * Since GEN8_MCR_SELECTOR contains dual-purpose bits which select both
-	 * to which subslice, or to which L3 bank, the respective mmio reads
-	 * will go, we have to find a common index which works for both
-	 * accesses.
-	 *
-	 * Case where we cannot find a common index fortunately should not
-	 * happen in production hardware, so we only emit a warning instead of
-	 * implementing something more complex that requires checking the range
-	 * of every MMIO read.
+	 * Although a platform may have subslices, we need to always steer
+	 * reads to the lowest instance that isn't fused off.  When Render
+	 * Power Gating is enabled, grabbing forcewake will only power up a
+	 * single subslice (the "minconfig") if there isn't a real workload
+	 * that needs to be run; this means that if we steer register reads to
+	 * one of the higher subslices, we run the risk of reading back 0's or
+	 * random garbage.
 	 */
+	subslice = __ffs(intel_sseu_get_subslices(sseu, slice));
 
-	if (GRAPHICS_VER(i915) >= 10 && is_power_of_2(sseu->slice_mask)) {
-		u32 l3_fuse =
-			intel_uncore_read(&i915->uncore, GEN10_MIRROR_FUSE3) &
-			GEN10_L3BANK_MASK;
-
-		drm_dbg(&i915->drm, "L3 fuse = %x\n", l3_fuse);
-		l3_en = ~(l3_fuse << GEN10_L3BANK_PAIR_COUNT | l3_fuse);
-	} else {
-		l3_en = ~0;
-	}
+	/*
+	 * If the subslice we picked above also steers us to a valid L3 bank,
+	 * then we can just rely on the default steering and won't need to
+	 * worry about explicitly re-steering L3BANK reads later.
+	 */
+	if (i915->gt.info.l3bank_mask & BIT(subslice))
+		i915->gt.steering_table[L3BANK] = NULL;
 
-	slice = fls(sseu->slice_mask) - 1;
-	subslice = fls(l3_en & intel_sseu_get_subslices(sseu, slice));
-	if (!subslice) {
-		drm_warn(&i915->drm,
-			 "No common index found between subslice mask %x and L3 bank mask %x!\n",
-			 intel_sseu_get_subslices(sseu, slice), l3_en);
-		subslice = fls(l3_en);
-		drm_WARN_ON(&i915->drm, !subslice);
-	}
-	subslice--;
-
-	if (GRAPHICS_VER(i915) >= 11) {
-		mcr = GEN11_MCR_SLICE(slice) | GEN11_MCR_SUBSLICE(subslice);
-		mcr_mask = GEN11_MCR_SLICE_MASK | GEN11_MCR_SUBSLICE_MASK;
-	} else {
-		mcr = GEN8_MCR_SLICE(slice) | GEN8_MCR_SUBSLICE(subslice);
-		mcr_mask = GEN8_MCR_SLICE_MASK | GEN8_MCR_SUBSLICE_MASK;
-	}
+	mcr = GEN11_MCR_SLICE(slice) | GEN11_MCR_SUBSLICE(subslice);
+	mcr_mask = GEN11_MCR_SLICE_MASK | GEN11_MCR_SUBSLICE_MASK;
 
 	drm_dbg(&i915->drm, "MCR slice/subslice = %x\n", mcr);
 
@@ -1019,8 +985,6 @@ wa_init_mcr(struct drm_i915_private *i915, struct i915_wa_list *wal)
 static void
 cnl_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
 {
-	wa_init_mcr(i915, wal);
-
 	/* WaInPlaceDecompressionHang:cnl */
 	wa_write_or(wal,
 		    GEN9_GAMT_ECO_REG_RW_IA,
@@ -1030,7 +994,7 @@ cnl_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
 static void
 icl_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
 {
-	wa_init_mcr(i915, wal);
+	icl_wa_init_mcr(i915, wal);
 
 	/* WaInPlaceDecompressionHang:icl */
 	wa_write_or(wal,
@@ -1112,7 +1076,7 @@ static void
 gen12_gt_workarounds_init(struct drm_i915_private *i915,
 			  struct i915_wa_list *wal)
 {
-	wa_init_mcr(i915, wal);
+	icl_wa_init_mcr(i915, wal);
 
 	/* Wa_14011060649:tgl,rkl,dg1,adls,adl-p */
 	wa_14011060649(i915, wal);