Hi Werner,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on drm-intel/for-linux-next]
[also build test ERROR on next-20210503]
[cannot apply to v5.12]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Werner-Sembach/drm-i915-display-Try-YCbCr420-color-when-RGB-fails/20210504-022344
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: x86_64-randconfig-r025-20210503 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 8f5a2a5836cc8e4c1def2bdeb022e7b496623439)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://github.com/0day-ci/linux/commit/8ff372234cbfe66eb5a59c2cda6a44961f5a9266
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Werner-Sembach/drm-i915-display-Try-YCbCr420-color-when-RGB-fails/20210504-022344
        git checkout 8ff372234cbfe66eb5a59c2cda6a44961f5a9266
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> drivers/gpu/drm/i915/display/intel_hdmi.c:2108:5: error: no previous prototype for function 'intel_hdmi_compute_output_format' [-Werror,-Wmissing-prototypes]
   int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
       ^
   drivers/gpu/drm/i915/display/intel_hdmi.c:2108:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
   ^
   static 
   1 error generated.


vim +/intel_hdmi_compute_output_format +2108 drivers/gpu/drm/i915/display/intel_hdmi.c

  2107	
> 2108	int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
  2109					     struct intel_crtc_state *crtc_state,
  2110					     const struct drm_connector_state *conn_state)
  2111	{
  2112		const struct drm_connector *connector = conn_state->connector;
  2113		const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
  2114		int ret;
  2115	
  2116		if (connector->ycbcr_420_allowed && drm_mode_is_420_only(&connector->display_info, adjusted_mode))
  2117			crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
  2118		else
  2119			crtc_state->output_format = INTEL_OUTPUT_FORMAT_RGB;
  2120	
  2121		ret = intel_hdmi_compute_clock(encoder, crtc_state);
  2122	
  2123		return ret;
  2124	}
  2125	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org