drm/i915/dsb: Introduce intel_dsb_reg_write_masked()

Add a function for emitting masked register writes.

Note that the mask is implemented through byte enables,
so can only mask off aligned 8bit sets of bits.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606191504.18099-10-ville.syrjala@linux.intel.comReviewed-by: Uma Shankar <uma.shankar@intel.com>

drivers/gpu/drm/i915/display/intel_dsb.c

@@ -234,6 +234,24 @@ void intel_dsb_reg_write(struct intel_dsb *dsb,
 	}
 }
 
+static u32 intel_dsb_mask_to_byte_en(u32 mask)
+{
+	return (!!(mask & 0xff000000) << 3 |
+		!!(mask & 0x00ff0000) << 2 |
+		!!(mask & 0x0000ff00) << 1 |
+		!!(mask & 0x000000ff) << 0);
+}
+
+/* Note: mask implemented via byte enables! */
+void intel_dsb_reg_write_masked(struct intel_dsb *dsb,
+				i915_reg_t reg, u32 mask, u32 val)
+{
+	intel_dsb_emit(dsb, val,
+		       (DSB_OPCODE_MMIO_WRITE << DSB_OPCODE_SHIFT) |
+		       (intel_dsb_mask_to_byte_en(mask) << DSB_BYTE_EN_SHIFT) |
+		       i915_mmio_reg_offset(reg));
+}
+
 void intel_dsb_noop(struct intel_dsb *dsb, int count)
 {
 	int i;

drivers/gpu/drm/i915/display/intel_dsb.h

@@ -19,6 +19,8 @@ void intel_dsb_finish(struct intel_dsb *dsb);
 void intel_dsb_cleanup(struct intel_dsb *dsb);
 void intel_dsb_reg_write(struct intel_dsb *dsb,
 			 i915_reg_t reg, u32 val);
+void intel_dsb_reg_write_masked(struct intel_dsb *dsb,
+				i915_reg_t reg, u32 mask, u32 val);
 void intel_dsb_noop(struct intel_dsb *dsb, int count);
 void intel_dsb_commit(struct intel_dsb *dsb,
 		      bool wait_for_vblank);