drm/radeon: Set depth on low mem to 16 bpp instead of 8 bpp

The radeon driver reduces the framebuffer resolution to 8bpp if a
device with less than 32MB VRAM is found.  This causes the framebuffer
to run in 8 bit paletted mode.  For a text console this is not an
issue as 256 different colors is more than one gets on a VGA text
console.  However this leads to a poor 8bit pseudo-color visual when
running X on fbdev, too, which is quite ugly.

In this patch, we try to give some moderate compromise: limit the
framebuffer bpp to 8 only when VRAM is 8MB or less, and use 16 bpp
otherwise for 32MB or less VRAM.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Egbert Eich <eich@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_fb.c

@@ -347,9 +347,12 @@ int radeon_fbdev_init(struct radeon_device *rdev)
 	if (list_empty(&rdev->ddev->mode_config.connector_list))
 		return 0;
 
-	/* select 8 bpp console on RN50 or 16MB cards */
+	/* select 8 bpp console on 8MB cards, or 16 bpp on RN50 or 32MB */
-	if (ASIC_IS_RN50(rdev) || rdev->mc.real_vram_size <= (32*1024*1024))
+	if (rdev->mc.real_vram_size <= (8*1024*1024))
 		bpp_sel = 8;
+	else if (ASIC_IS_RN50(rdev) ||
+		 rdev->mc.real_vram_size <= (32*1024*1024))
+		bpp_sel = 16;
 
 	rfbdev = kzalloc(sizeof(struct radeon_fbdev), GFP_KERNEL);
 	if (!rfbdev)