Hello Ankit Nautiyal,
Commit 1c56e9a39833 ("drm/i915/dp: Get optimal link config to have
best compressed bpp") from Aug 17, 2023 (linux-next), leads to the
following Smatch static checker warning:
drivers/gpu/drm/i915/display/intel_dp.c:2481 intel_dp_dsc_compute_pipe_bpp_limits()
warn: always clamps to 24
drivers/gpu/drm/i915/display/intel_dp.c
2472 static void
2473 intel_dp_dsc_compute_pipe_bpp_limits(struct intel_dp *intel_dp,
2474 struct link_config_limits *limits)
2475 {
2476 struct intel_display *display = to_intel_display(intel_dp);
2477 int dsc_min_bpc = intel_dp_dsc_min_src_input_bpc();
2478 int dsc_max_bpc = intel_dp_dsc_max_src_input_bpc(display);
2479
2480 limits->pipe.max_bpp = clamp(limits->pipe.max_bpp, dsc_min_bpc * 3, dsc_max_bpc * 3);
--> 2481 limits->pipe.min_bpp = clamp(limits->pipe.min_bpp, dsc_min_bpc * 3, dsc_max_bpc * 3);
2482 }
This is an unpublished static checker warning that complains about weird
clamps() so it only just started showing up now. The problem is a
mismatch between intel_dp_min_bpp() and intel_dp_dsc_min_src_input_bpc().
In intel_dp_min_bpp() it uses "6 * 3" but then that gets overwriten with
"8 * 3" eventually. The warning is that "6 * 3" might be pointless?
I haven't followed the code totally, but it seems like potentially the
checker is correct.
drivers/gpu/drm/i915/display/intel_dp.c
1175 int intel_dp_min_bpp(enum intel_output_format output_format)
1176 {
1177 if (output_format == INTEL_OUTPUT_FORMAT_RGB)
1178 return 6 * 3;
^^^^^
Is this pointless? Should we just always return "8 * 3" since
that's what it's clamped to in the end?
1179 else
1180 return 8 * 3;
1181 }
drivers/gpu/drm/i915/display/intel_dp.c
2161 int intel_dp_dsc_min_src_input_bpc(void)
2162 {
2163 /* Min DSC Input BPC for ICL+ is 8 */
2164 return 8;
This 8 becomes "8 * 3" in the caller.
2165 }
regards,
dan carpenter
