[PATCH v2 5/5] drm: WARN when calling drm_format_info() for an unsupported format

[Laurent Pinchart]

The format helpers have historically treated unsupported formats as part
of the default case, returning values that are likely wrong. We can't
change this behaviour now without risking breaking drivers in difficult
to detect ways, but we can WARN on unsupported formats to catch faulty
callers.

The only exception is the framebuffer_check() function that calls
drm_format_info() to validate the format passed from userspace. This is
a valid use case that shouldn't generate a warning.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 drivers/gpu/drm/drm_crtc.c   |  2 +-
 drivers/gpu/drm/drm_fourcc.c | 32 ++++++++++++++++++++++++--------
 include/drm/drm_fourcc.h     |  1 +
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 73fa7f2a1a04..1777ab37890a 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -3178,7 +3178,7 @@ static int framebuffer_check(const struct drm_mode_fb_cmd2 *r)
 	const struct drm_format_info *info;
 	int i;
 
-	info = drm_format_info(r->pixel_format & ~DRM_FORMAT_BIG_ENDIAN);
+	info = __drm_format_info(r->pixel_format & ~DRM_FORMAT_BIG_ENDIAN);
 	if (!info) {
 		DRM_DEBUG_KMS("bad framebuffer format %s\n",
 			      drm_get_format_name(r->pixel_format));
diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 0c2cdab7f974..1dfbcaa6cd03 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -61,15 +61,11 @@ const char *drm_get_format_name(uint32_t format)
 }
 EXPORT_SYMBOL(drm_get_format_name);
 
-/**
- * drm_format_info - query information for a given format
- * @format: pixel format (DRM_FORMAT_*)
- *
- * Returns:
- * The instance of struct drm_format_info that describes the pixel format, or
- * NULL if the format is unsupported.
+/*
+ * Internal function to query information for a given format. See
+ * drm_format_info() for the public API.
  */
-const struct drm_format_info *drm_format_info(u32 format)
+const struct drm_format_info *__drm_format_info(u32 format)
 {
 	static const struct drm_format_info formats[] = { 
 		{ .format = DRM_FORMAT_C8,		.depth = 8,  .bpp = 8,  .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1 },
@@ -143,6 +139,26 @@ const struct drm_format_info *drm_format_info(u32 format)
 
 	return NULL;
 }
+
+/**
+ * drm_format_info - query information for a given format
+ * @format: pixel format (DRM_FORMAT_*)
+ *
+ * The caller should only pass a supported pixel format to this function.
+ * Unsupported pixel formats will generate a warning in the kernel log.
+ *
+ * Returns:
+ * The instance of struct drm_format_info that describes the pixel format, or
+ * NULL if the format is unsupported.
+ */
+const struct drm_format_info *drm_format_info(u32 format)
+{
+	const struct drm_format_info *info;
+
+	info = __drm_format_info(format);
+	WARN_ON(!info);
+	return info;
+}
 EXPORT_SYMBOL(drm_format_info);
 
 /**
diff --git a/include/drm/drm_fourcc.h b/include/drm/drm_fourcc.h
index d33411bd19b1..ee22dff0786e 100644
--- a/include/drm/drm_fourcc.h
+++ b/include/drm/drm_fourcc.h
@@ -45,6 +45,7 @@ struct drm_format_info {
 	u8 vsub;
 };
 
+const struct drm_format_info *__drm_format_info(u32 format);
 const struct drm_format_info *drm_format_info(u32 format);
 void drm_fb_get_bpp_depth(uint32_t format, unsigned int *depth, int *bpp);
 int drm_format_num_planes(uint32_t format);
-- 
Regards,

Laurent Pinchart