drm/radeon: add a delay after ATPX dGPU power off

commit d814b24f upstream.

ATPX dGPU power control requires a 200ms delay between
power off and on.  This should fix dGPU failures on
resume from power off.
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Willy Tarreau <w@1wt.eu>

drivers/gpu/drm/radeon/radeon_atpx_handler.c

@@ -11,6 +11,7 @@
 #include <acpi/acpi.h>
 #include <acpi/acpi_bus.h>
 #include <linux/pci.h>
+#include <linux/delay.h>
 
 #include "radeon_acpi.h"
 
@@ -252,6 +253,10 @@ static int radeon_atpx_set_discrete_state(struct radeon_atpx *atpx, u8 state)
 		if (!info)
 			return -EIO;
 		kfree(info);
+
+		/* 200ms delay is required after off */
+		if (state == 0)
+			msleep(200);
 	}
 	return 0;
 }