[PATCH v4 01/11] drm/fourcc: Add warning for bad bpp

Tomi Valkeinen
2025-03-26T13:23:20Z

drm_format_info_bpp() cannot be used for formats which do not have an
integer bits-per-pixel in a pixel block.

E.g. DRM_FORMAT_XV15's (not yet in upstream) plane 0 has three 10-bit
pixels (Y components), and two padding bits, in a 4 byte block. That is
10.666... bits per pixel when considering the whole 4 byte block, which
is what drm_format_info_bpp() does. Thus a driver that supports such
formats cannot use drm_format_info_bpp(),

It is a driver bug if this happens, but so handle wrong calls by
printing a warning and returning 0.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
drivers/gpu/drm/drm_fourcc.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 3a94ca211f9c..2f5781f5dcda 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -454,12 +454,20 @@ EXPORT_SYMBOL(drm_format_info_block_height);
*/
unsigned int drm_format_info_bpp(const struct drm_format_info *info, int plane)
{
+ unsigned int block_size;
+
if (!info || plane < 0 || plane >= info->num_planes)
return 0;

- return info->char_per_block[plane] * 8 /
- (drm_format_info_block_width(info, plane) *
- drm_format_info_block_height(info, plane));
+ block_size = drm_format_info_block_width(info, plane) *
+ drm_format_info_block_height(info, plane);
+
+ if (info->char_per_block[plane] * 8 % block_size) {
+ pr_warn("unable to return an integer bpp\n");
+ return 0;
+ }
+
+ return info->char_per_block[plane] * 8 / block_size;
}
EXPORT_SYMBOL(drm_format_info_bpp);

--
2.43.0