drm/i915: Add GT support for multiple types of multicast steering

Although most of our multicast registers are replicated per-subslice, we
also have a small number of multicast registers that are replicated
per-l3 bank instead.  For both types of multicast registers we need to
make sure we steer reads of these registers to a valid instance.
Ideally we'd like to find a specific instance ID that would steer reads
of either type of multicast register to a valid instance (i.e., not
fused off and not powered down), but sometimes the combination of
part-specific fusing and the additional restrictions imposed by Render
Power Gating make it impossible to find any overlap between the set of
valid subslices and valid l3 banks.  This problem will become even more
noticeable on our upcoming platforms since they will be adding
additional types of multicast registers with new types of replication
and rules for finding valid instances for reads.

To handle this we'll continue to pick a suitable subslice instance at
driver startup and program this as the default (sliceid,subsliceid)
setting in the steering control register (0xFDC).  In cases where we
need to read another type of multicast GT register, but the default
subslice steering would not correspond to a valid instance, we'll
explicitly re-steer the single read to a valid value, perform the read,
and then reset the steering to it's "subslice" default.

This patch adds the general functionality to prepare for this explicit
steering of other multicast register types.  We'll plug L3 bank steering
into this in the next patch, and then add additional types of multicast
registers when the support for our next upcoming platform arrives.

v2:
 - Use entry->end==0 as table terminator.  (Rodrigo)
 - Grab forcewake in wa_list_verify() now that we're using accessors
   that assume forcewake is already held.

v3:
 - Fix loop condition when iterating over steering range tables.
   (Rodrigo)

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/20210617211425.1943662-3-matthew.d.roper@intel.com

1 files changed, 84 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index 67ef057ae918..1c7ca7a090ab 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -701,6 +701,90 @@ void intel_gt_driver_late_release(struct intel_gt *gt)
 	intel_engines_free(gt);
 }
 
+/**
+ * intel_gt_reg_needs_read_steering - determine whether a register read
+ *     requires explicit steering
+ * @gt: GT structure
+ * @reg: the register to check steering requirements for
+ * @type: type of multicast steering to check
+ *
+ * Determines whether @reg needs explicit steering of a specific type for
+ * reads.
+ *
+ * Returns false if @reg does not belong to a register range of the given
+ * steering type, or if the default (subslice-based) steering IDs are suitable
+ * for @type steering too.
+ */
+static bool intel_gt_reg_needs_read_steering(struct intel_gt *gt,
+					     i915_reg_t reg,
+					     enum intel_steering_type type)
+{
+	const u32 offset = i915_mmio_reg_offset(reg);
+	const struct intel_mmio_range *entry;
+
+	if (likely(!intel_gt_needs_read_steering(gt, type)))
+		return false;
+
+	for (entry = gt->steering_table[type]; entry->end; entry++) {
+		if (offset >= entry->start && offset <= entry->end)
+			return true;
+	}
+
+	return false;
+}
+
+/**
+ * intel_gt_get_valid_steering - determines valid IDs for a class of MCR steering
+ * @gt: GT structure
+ * @type: multicast register type
+ * @sliceid: Slice ID returned
+ * @subsliceid: Subslice ID returned
+ *
+ * Determines sliceid and subsliceid values that will steer reads
+ * of a specific multicast register class to a valid value.
+ */
+static void intel_gt_get_valid_steering(struct intel_gt *gt,
+					enum intel_steering_type type,
+					u8 *sliceid, u8 *subsliceid)
+{
+	switch (type) {
+	default:
+		MISSING_CASE(type);
+		*sliceid = 0;
+		*subsliceid = 0;
+	}
+}
+
+/**
+ * intel_gt_read_register_fw - reads a GT register with support for multicast
+ * @gt: GT structure
+ * @reg: register to read
+ *
+ * This function will read a GT register.  If the register is a multicast
+ * register, the read will be steered to a valid instance (i.e., one that
+ * isn't fused off or powered down by power gating).
+ *
+ * Returns the value from a valid instance of @reg.
+ */
+u32 intel_gt_read_register_fw(struct intel_gt *gt, i915_reg_t reg)
+{
+	int type;
+	u8 sliceid, subsliceid;
+
+	for (type = 0; type < NUM_STEERING_TYPES; type++) {
+		if (intel_gt_reg_needs_read_steering(gt, reg, type)) {
+			intel_gt_get_valid_steering(gt, type, &sliceid,
+						    &subsliceid);
+			return intel_uncore_read_with_mcr_steering_fw(gt->uncore,
+								      reg,
+								      sliceid,
+								      subsliceid);
+		}
+	}
+
+	return intel_uncore_read_fw(gt->uncore, reg);
+}
+
 void intel_gt_info_print(const struct intel_gt_info *info,
 			 struct drm_printer *p)
 {