linux-kernel - [PATCH v2 01/10] drm/fourcc: Add warning for bad bpp

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Message-Id: <20250115-xilinx-formats-v2-1-160327ca652a@ideasonboard.com>
Date: Wed, 15 Jan 2025 11:03:30 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Vishal Sagar <vishal.sagar@....com>, 
 Anatoliy Klymenko <anatoliy.klymenko@....com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Michal Simek <michal.simek@....com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: [PATCH v2 01/10] drm/fourcc: Add warning for bad bpp

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.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
---
 drivers/gpu/drm/drm_fourcc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 193cf8ed7912..e84c4ed6928c 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -429,6 +429,13 @@ unsigned int drm_format_info_bpp(const struct drm_format_info *info, int plane)
 	if (!info || plane < 0 || plane >= info->num_planes)
 		return 0;
 
+	if (info->char_per_block[plane] * 8 %
+	    (drm_format_info_block_width(info, plane) *
+	     drm_format_info_block_height(info, plane))) {
+		pr_warn("unable to return an integer bpp\n");
+		return 0;
+	}
+
 	return info->char_per_block[plane] * 8 /
 	       (drm_format_info_block_width(info, plane) *
 		drm_format_info_block_height(info, plane));

-- 
2.43.0