drm/radeon/kms: fix MSI re-arm on rv370+

MSI_REARM_EN register is a write only trigger register.
There is no need RMW when re-arming.

May fix:
https://bugs.freedesktop.org/show_bug.cgi?id=41668Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
CC: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/r100.c

@@ -789,9 +789,7 @@ int r100_irq_process(struct radeon_device *rdev)
 			WREG32(RADEON_AIC_CNTL, msi_rearm | RS400_MSI_REARM);
 			break;
 		default:
-			msi_rearm = RREG32(RADEON_MSI_REARM_EN) & ~RV370_MSI_REARM_EN;
-			WREG32(RADEON_MSI_REARM_EN, msi_rearm);
-			WREG32(RADEON_MSI_REARM_EN, msi_rearm | RV370_MSI_REARM_EN);
+			WREG32(RADEON_MSI_REARM_EN, RV370_MSI_REARM_EN);
 			break;
 		}
 	}

drivers/gpu/drm/radeon/rs600.c

@@ -684,9 +684,7 @@ int rs600_irq_process(struct radeon_device *rdev)
 			WREG32(RADEON_BUS_CNTL, msi_rearm | RS600_MSI_REARM);
 			break;
 		default:
-			msi_rearm = RREG32(RADEON_MSI_REARM_EN) & ~RV370_MSI_REARM_EN;
-			WREG32(RADEON_MSI_REARM_EN, msi_rearm);
-			WREG32(RADEON_MSI_REARM_EN, msi_rearm | RV370_MSI_REARM_EN);
+			WREG32(RADEON_MSI_REARM_EN, RV370_MSI_REARM_EN);
 			break;
 		}
 	}