drm/i915/gt: Add intel_gt_mcr_multicast_rmw() operation

There are cases where we wish to read from any non-terminated MCR
register instance (or the primary instance in the case of GAM ranges),
clear/set some bits, and then write the value back out to the register
in a multicast manner.  Adding a "multicast RMW" will avoid the need to
open-code this.

v2:
 - Return a u32 to align with the recent change to intel_uncore_rmw.
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221014230239.1023689-6-matthew.d.roper@intel.com

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

@@ -302,6 +302,34 @@ void intel_gt_mcr_multicast_write_fw(struct intel_gt *gt, i915_reg_t reg, u32 va
 	intel_uncore_write_fw(gt->uncore, reg, value);
 }
 
+/**
+ * intel_gt_mcr_multicast_rmw - Performs a multicast RMW operations
+ * @gt: GT structure
+ * @reg: the MCR register to read and write
+ * @clear: bits to clear during RMW
+ * @set: bits to set during RMW
+ *
+ * Performs a read-modify-write on an MCR register in a multicast manner.
+ * This operation only makes sense on MCR registers where all instances are
+ * expected to have the same value.  The read will target any non-terminated
+ * instance and the write will be applied to all instances.
+ *
+ * This function assumes the caller is already holding any necessary forcewake
+ * domains; use intel_gt_mcr_multicast_rmw() in cases where forcewake should
+ * be obtained automatically.
+ *
+ * Returns the old (unmodified) value read.
+ */
+u32 intel_gt_mcr_multicast_rmw(struct intel_gt *gt, i915_reg_t reg,
+			       u32 clear, u32 set)
+{
+	u32 val = intel_gt_mcr_read_any(gt, reg);
+
+	intel_gt_mcr_multicast_write(gt, reg, (val & ~clear) | set);
+
+	return val;
+}
+
 /*
  * reg_needs_read_steering - determine whether a register read requires
  *     explicit steering

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

@@ -24,6 +24,9 @@ void intel_gt_mcr_multicast_write(struct intel_gt *gt,
 void intel_gt_mcr_multicast_write_fw(struct intel_gt *gt,
 				     i915_reg_t reg, u32 value);
 
+u32 intel_gt_mcr_multicast_rmw(struct intel_gt *gt, i915_reg_t reg,
+			       u32 clear, u32 set);
+
 void intel_gt_mcr_get_nonterminated_steering(struct intel_gt *gt,
 					     i915_reg_t reg,
 					     u8 *group, u8 *instance);