[PATCH] drm/amd/display: Avoid enum conversion warning

[PATCH] drm/amd/display: Avoid enum conversion warning

[Nathan Chancellor]

Clang warns (or errors with CONFIG_WERROR=y) when performing arithmetic
with different enumerated types, which is usually a bug:

    drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_dpia_bw.c:548:24: error: arithmetic between different enumeration types ('const enum dc_link_rate' and 'const enum dc_lane_count') [-Werror,-Wenum-enum-conversion]
      548 |                         link_cap->link_rate * link_cap->lane_count * LINK_RATE_REF_FREQ_IN_KHZ * 8;
          |                         ~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~
    1 error generated.

In this case, there is not a problem because the enumerated types are
basically treated as '#define' values. Add an explicit cast to an
integral type to silence the warning.

Closes: https://github.com/ClangBuiltLinux/linux/issues/1976
Fixes: 5f3bce13266e ("drm/amd/display: Request usb4 bw for mst streams")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
index 4ef1a6a1d129..dd0d2b206462 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
@@ -544,8 +544,9 @@ int link_dp_dpia_get_dp_overhead_in_dp_tunneling(struct dc_link *link)
 		 */
 		const struct dc_link_settings *link_cap =
 			dc_link_get_link_cap(link);
-		uint32_t link_bw_in_kbps =
-			link_cap->link_rate * link_cap->lane_count * LINK_RATE_REF_FREQ_IN_KHZ * 8;
+		uint32_t link_bw_in_kbps = (uint32_t)link_cap->link_rate *
+					   (uint32_t)link_cap->lane_count *
+					   LINK_RATE_REF_FREQ_IN_KHZ * 8;
 		link_mst_overhead = (link_bw_in_kbps / 64) + ((link_bw_in_kbps % 64) ? 1 : 0);
 	}
 

---
base-commit: 6e7a29f011ac03a765f53844f7c3f04cdd421715
change-id: 20240110-amdgpu-display-enum-enum-conversion-e2451adbf4a7

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

Re: [PATCH] drm/amd/display: Avoid enum conversion warning

[Alex Deucher]

Applied.  Thanks!

On Wed, Jan 10, 2024 at 3:56 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Clang warns (or errors with CONFIG_WERROR=y) when performing arithmetic
> with different enumerated types, which is usually a bug:
>
>     drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_dpia_bw.c:548:24: error: arithmetic between different enumeration types ('const enum dc_link_rate' and 'const enum dc_lane_count') [-Werror,-Wenum-enum-conversion]
>       548 |                         link_cap->link_rate * link_cap->lane_count * LINK_RATE_REF_FREQ_IN_KHZ * 8;
>           |                         ~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~
>     1 error generated.
>
> In this case, there is not a problem because the enumerated types are
> basically treated as '#define' values. Add an explicit cast to an
> integral type to silence the warning.
>
> Closes: https://github.com/ClangBuiltLinux/linux/issues/1976
> Fixes: 5f3bce13266e ("drm/amd/display: Request usb4 bw for mst streams")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
> index 4ef1a6a1d129..dd0d2b206462 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
> +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
> @@ -544,8 +544,9 @@ int link_dp_dpia_get_dp_overhead_in_dp_tunneling(struct dc_link *link)
>                  */
>                 const struct dc_link_settings *link_cap =
>                         dc_link_get_link_cap(link);
> -               uint32_t link_bw_in_kbps =
> -                       link_cap->link_rate * link_cap->lane_count * LINK_RATE_REF_FREQ_IN_KHZ * 8;
> +               uint32_t link_bw_in_kbps = (uint32_t)link_cap->link_rate *
> +                                          (uint32_t)link_cap->lane_count *
> +                                          LINK_RATE_REF_FREQ_IN_KHZ * 8;
>                 link_mst_overhead = (link_bw_in_kbps / 64) + ((link_bw_in_kbps % 64) ? 1 : 0);
>         }
>
>
> ---
> base-commit: 6e7a29f011ac03a765f53844f7c3f04cdd421715
> change-id: 20240110-amdgpu-display-enum-enum-conversion-e2451adbf4a7
>
> Best regards,
> --
> Nathan Chancellor <nathan@kernel.org>
>