drm/i915: Disable display interrupts during display IRQ handler

During the Display Interrupt Service routine the Display Interrupt
Enable bit must be disabled, The interrupts handled, then the
Display Interrupt Enable bit must be set to prevent possible missed
interrupts.

Bspec: 49212
V2: Change Title to remove SDE reference.
V3: Fix TAB spacing.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Aditya Swarup <aditya.swarup@intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NClint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: NLucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191121201455.2558-1-clinton.a.taylor@intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -2484,7 +2484,11 @@ __gen11_irq_handler(struct drm_i915_private * const i915,
 		 * GEN11_DISPLAY_INT_CTL has same format as GEN8_MASTER_IRQ
 		 * for the display related bits.
 		 */
+		raw_reg_write(regs, GEN11_DISPLAY_INT_CTL, 0x0);
 		gen8_de_irq_handler(i915, disp_ctl);
+		raw_reg_write(regs, GEN11_DISPLAY_INT_CTL,
+			      GEN11_DISPLAY_IRQ_ENABLE);
+
 		enable_rpm_wakeref_asserts(&i915->runtime_pm);
 	}