Re: [PATCH] drm/amd/display: Fix an uninitialized index variable

On Thu, Feb 25, 2021 at 7:01 AM Arnd Bergmann arnd@kernel.org wrote:

From: Arnd Bergmann arnd@arndb.de

clang points out that the new logic uses an always-uninitialized array index:

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:9810:38: warning: variable 'i' is uninitialized when used here [-Wuninitialized] timing = &edid->detailed_timings[i]; ^ drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:9720:7: note: initialize the variable 'i' to silence this warning

My best guess is that the index should have been returned by the parse_hdmi_amd_vsdb() function that walks an array here, so do that.

Fixes: f9b4f20c4777 ("drm/amd/display: Add Freesync HDMI support to DM") Signed-off-by: Arnd Bergmann arnd@arndb.de

---

.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index b19b93c74bae..667c0d52dbfa 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -9736,7 +9736,7 @@ static bool parse_edid_cea(struct amdgpu_dm_connector *aconnector, return false; }

-static bool parse_hdmi_amd_vsdb(struct amdgpu_dm_connector *aconnector, +static int parse_hdmi_amd_vsdb(struct amdgpu_dm_connector *aconnector, struct edid *edid, struct amdgpu_hdmi_vsdb_info *vsdb_info) { uint8_t *edid_ext = NULL; @@ -9746,7 +9746,7 @@ static bool parse_hdmi_amd_vsdb(struct amdgpu_dm_connector *aconnector, /*----- drm_find_cea_extension() -----*/ /* No EDID or EDID extensions */ if (edid == NULL || edid->extensions == 0)

•           return false;
  

•           return -ENODEV;
  
    /* Find CEA extension */
    for (i = 0; i < edid->extensions; i++) {
  

@@ -9756,14 +9756,15 @@ static bool parse_hdmi_amd_vsdb(struct amdgpu_dm_connector *aconnector, }

    if (i == edid->extensions)

•           return false;
  

•           return -ENODEV;
  
    /*----- cea_db_offsets() -----*/
    if (edid_ext[0] != CEA_EXT)
  

•           return false;
  

•           return -ENODEV;
  
    valid_vsdb_found = parse_edid_cea(aconnector, edid_ext, EDID_LENGTH, vsdb_info);
  

•   return valid_vsdb_found;
  

•   return valid_vsdb_found ? i : -ENODEV;
  

Thanks for the patch!

I don't think we need a local variable to store the return value from one function call that's immediately returned, ie.

return parse_edid_cea(aconnector, edid_ext, EDID_LENGTH, vsdb_info) ? i : -ENODEV;

would suffice, but the patch is still fine as is.

Reviewed-by: Nick Desaulniers ndesaulniers@google.com

}

void amdgpu_dm_update_freesync_caps(struct drm_connector *connector, @@ -9781,7 +9782,6 @@ void amdgpu_dm_update_freesync_caps(struct drm_connector *connector, struct amdgpu_device *adev = drm_to_adev(dev); bool freesync_capable = false; struct amdgpu_hdmi_vsdb_info vsdb_info = {0};

•   bool hdmi_valid_vsdb_found = false;
  
    if (!connector->state) {
            DRM_ERROR("%s - Connector has no state", __func__);
  

@@ -9857,8 +9857,8 @@ void amdgpu_dm_update_freesync_caps(struct drm_connector *connector, } } } else if (edid && amdgpu_dm_connector->dc_sink->sink_signal == SIGNAL_TYPE_HDMI_TYPE_A) {

•           hdmi_valid_vsdb_found = parse_hdmi_amd_vsdb(amdgpu_dm_connector, edid, &vsdb_info);
  

•           if (hdmi_valid_vsdb_found && vsdb_info.freesync_supported) {
  

•           i = parse_hdmi_amd_vsdb(amdgpu_dm_connector, edid, &vsdb_info);
  

•           if (i >= 0 && vsdb_info.freesync_supported) {
  

reusing `i` here is safe, for now, but reuse of variables like this in separate branches like this might not get noticed if the function is amended in the future.

                    timing  = &edid->detailed_timings[i];
                    data    = &timing->data.other_data;

-- 2.29.2