clk: qcom: rcg2: compute 2d using duty fraction directly

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[ Upstream commit d6205a1878 ]

The duty-cycle calculation in clk_rcg2_set_duty_cycle() currently
derives an intermediate percentage `duty_per = (num * 100) / den` and
then computes:

    d = DIV_ROUND_CLOSEST(n * duty_per * 2, 100);

This introduces integer truncation at the percentage step (division by
`den`) and a redundant scaling by 100, which can reduce precision for
large `den` and skew the final rounding.

Compute `2d` directly from the duty fraction to preserve precision and
avoid the unnecessary scaling:

    d = DIV_ROUND_CLOSEST(n * duty->num * 2, duty->den);

This keeps the intended formula `d ≈ n * 2 * (num/den)` while performing
a single, final rounded division, improving accuracy especially for small
duty cycles or large denominators. It also removes the unused `duty_per`
variable, simplifying the code.

There is no functional changes beyond improved numerical accuracy.

Fixes: 7f891faf59 ("clk: qcom: clk-rcg2: Add support for duty-cycle for RCG")
Signed-off-by: Taniya Das <taniya.das@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260105-duty_cycle_precision-v2-1-d1d466a6330a@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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This commit is contained in:

Taniya Das 2026-01-05 16:09:50 +05:30 • committed by Greg Kroah-Hartman

parent aa14e76038

commit f7b0686119

1 changed files with 2 additions and 4 deletions

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drivers/clk/qcom/clk-rcg2.c

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