drm: move allocation out of drm_get_format_name()

The function's behaviour was changed in 90844f00049e, without changing
its signature, causing people to keep using it the old way without
realising they were now leaking memory.
Rob Clark also noticed it was also allocating GFP_KERNEL memory in
atomic contexts, breaking them.

Instead of having to allocate GFP_ATOMIC memory and fixing the callers
to make them cleanup the memory afterwards, let's change the function's
signature by having the caller take care of the memory and passing it to
the function.
The new parameter is a single-field struct in order to enforce the size
of its buffer and help callers to correctly manage their memory.

Fixes: 90844f00049e ("drm: make drm_get_format_name thread-safe")
Cc: Rob Clark <robdclark@gmail.com>
Cc: Christian König <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Sinclair Yeh <syeh@vmware.com> (vmwgfx)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161112011309.9799-1-eric@engestrom.ch

1 files changed, 5 insertions, 9 deletions

diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index cbb8b77c363c..90d2cc8da8eb 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -79,17 +79,13 @@ uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth)
 EXPORT_SYMBOL(drm_mode_legacy_fb_format);
 
 /**
- * drm_get_format_name - return a string for drm fourcc format
+ * drm_get_format_name - fill a string with a drm fourcc format's name
  * @format: format to compute name of
- *
- * Note that the buffer returned by this function is owned by the caller
- * and will need to be freed using kfree().
+ * @buf: caller-supplied buffer
  */
-char *drm_get_format_name(uint32_t format)
+const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf)
 {
-	char *buf = kmalloc(32, GFP_KERNEL);
-
-	snprintf(buf, 32,
+	snprintf(buf->str, sizeof(buf->str),
 		 "%c%c%c%c %s-endian (0x%08x)",
 		 printable_char(format & 0xff),
 		 printable_char((format >> 8) & 0xff),
@@ -98,7 +94,7 @@ char *drm_get_format_name(uint32_t format)
 		 format & DRM_FORMAT_BIG_ENDIAN ? "big" : "little",
 		 format);
 
-	return buf;
+	return buf->str;
 }
 EXPORT_SYMBOL(drm_get_format_name);