[PATCH] drm/amd/display: Avoid -Wenum-float-conversion in add_margin_and_round_to_dfs_grainularity()

[Nathan Chancellor]

When building with clang 19 or newer (which strengthened some of the
enum conversion warnings for C), there is a warning (or error with
CONFIG_WERROR=y) around doing arithmetic with an enumerated type and a
floating point expression.

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c:181:58: error: arithmetic between enumeration type 'enum dentist_divider_range' and floating-point type 'double' [-Werror,-Wenum-float-conversion]
    181 |         divider = (unsigned int)(DFS_DIVIDER_RANGE_SCALE_FACTOR * (vco_freq_khz / clock_khz));
        |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

This conversion is expected due to the nature of the enumerated value
and definition, so silence the warning by casting the enumeration to an
integer explicitly to make it clear to the compiler.

Fixes: 3df48ddedee4 ("drm/amd/display: Add new DCN401 sources")
Signed-off-by: Nathan Chancellor <nathan at kernel.org>
---
Alternatively, perhaps the potential truncation could happen before the
multiplication?

  divider = DFS_DIVIDER_RANGE_SCALE_FACTOR * (unsigned int)(vco_freq_khz / clock_khz);

I suspect the result of the division is probably not very large
(certainly not within UINT_MAX / 4), so I would not expect the
multiplication to overflow, but I was not sure so I decided to take the
safer, NFC change. I am happy to respin as necessary.
---
 .../gpu/drm/amd/display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c
index e6698ee65843..65eb0187e965 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_dpmm/dml2_dpmm_dcn4.c
@@ -178,7 +178,7 @@ static bool add_margin_and_round_to_dfs_grainularity(double clock_khz, double ma
 
 	clock_khz *= 1.0 + margin;
 
-	divider = (unsigned int)(DFS_DIVIDER_RANGE_SCALE_FACTOR * (vco_freq_khz / clock_khz));
+	divider = (unsigned int)((int)DFS_DIVIDER_RANGE_SCALE_FACTOR * (vco_freq_khz / clock_khz));
 
 	/* we want to floor here to get higher clock than required rather than lower */
 	if (divider < DFS_DIVIDER_RANGE_2_START) {

---
base-commit: d60dc4dd72412d5d9566fdf391e4202b05f88912
change-id: 20240424-amdgpu-display-dcn401-enum-float-conversion-c09cc1826ea2

Best regards,
-- 
Nathan Chancellor <nathan at kernel.org>