drm/amd/display: Cast DP DTO pixel clock math to avoid overflow and narrowing

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[Why]
Commit 0421fc6ab3 ("drm/amd/display: fix __udivdi3 link error") switched
get_dp_dto_frequency_100hz() and dcn401_get_dp_dto_frequency_100hz() to
div_u64() but dropped the original explicit casts, leaving two issues:

- In get_dp_dto_frequency_100hz(), "clock_hz * dp_dto_ref_khz * 10" is
  computed in 32-bit unsigned arithmetic (both operands are unsigned int)
  before being stored into the u64 temp, so the product can overflow
  before it is widened (flagged by Coverity OVERFLOW_BEFORE_WIDEN).
- div_u64() returns a u64 that is assigned directly to the unsigned int
  *pixel_clk_100hz, an implicit narrowing conversion that trips
  -Wconversion (possible loss of data) on stricter builds.

[How]
Cast clock_hz to unsigned long long so the multiplication is performed in
64-bit, and make the u64 -> unsigned int narrowing explicit with an
(unsigned int) cast on the div_u64() results in both functions. The
computed values are unchanged.

Fixes: 0421fc6ab3 ("drm/amd/display: fix __udivdi3 link error")
Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: James Lin <PingLei.Lin@amd.com>
Signed-off-by: Chenyu Chen <chen-yu.chen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

...

This commit is contained in:

James Lin 2026-08-13 16:50:28 +08:00 • committed by Alex Deucher

parent d4e5df4d7e

commit 0575f53925

1 changed files with 3 additions and 3 deletions

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drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c

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