drm/xe/irq: Don't clobber display interrupts on multi-tile platforms

Although our only multi-tile platform today (PVC) doesn't support
display, it's possible that some future multi-tile platform will.
If/when this happens, display interrupts (both traditional display and
ASLE backlight interrupts raised as a Gunit interrupt) should be
delivered to the primary tile.  Save away tile0's master_ctl value so
that it can still be used for display interrupt handling after the GT
loop.
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230401002106.588656-9-matthew.d.roper@intel.comSigned-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_irq.c

@@ -350,7 +350,7 @@ static irqreturn_t dg1_irq_handler(int irq, void *arg)
 {
 	struct xe_device *xe = arg;
 	struct xe_gt *gt;
-	u32 master_tile_ctl, master_ctl = 0, gu_misc_iir;
+	u32 master_tile_ctl, master_ctl = 0, tile0_master_ctl = 0, gu_misc_iir;
 	long unsigned int intr_dw[2];
 	u32 identity[32];
 	u8 id;
@@ -384,9 +384,17 @@ static irqreturn_t dg1_irq_handler(int irq, void *arg)
 		if (!xe_gt_is_media_type(gt))
 			xe_mmio_write32(gt, GFX_MSTR_IRQ.reg, master_ctl);
 		gt_irq_handler(xe, gt, master_ctl, intr_dw, identity);
+
+		/*
+		 * Save primary tile's master interrupt register for display
+		 * processing below.
+		 */
+		if (id == 0)
+			tile0_master_ctl = master_ctl;
 	}
 
-	gu_misc_iir = gu_misc_irq_ack(gt, master_ctl);
+	/* Gunit GSE interrupts can trigger display backlight operations */
+	gu_misc_iir = gu_misc_irq_ack(gt, tile0_master_ctl);
 
 	dg1_intr_enable(xe, false);