firmware: arm_scmi: Use 64-bit division for clock rate rounding

SCMI clock range descriptors report rates as 64-bit values. When handling
a range clock, scmi_clock_determine_rate() rounds the requested rate up to
the next supported step using the SCMI RATE_STEP value.

The current code uses div64_ul() for this calculation. Since div64_ul()
takes an unsigned long divisor, the 64-bit RATE_STEP value can be truncated
on 32-bit builds. In the worst case, a non-zero 64-bit step can be narrowed
to zero before the division.

Store RATE_STEP in a u64, reject a malformed zero step, and use
DIV64_U64_ROUND_UP() so the divisor is handled as a 64-bit value.

This does not change behavior for valid firmware reporting a non-zero step
that fits in unsigned long.

Tested on Xunlong Orange Pi 5 Plus / RK3588 with SCMI over SMC. SCMI
clocks probed successfully before and after the change. SCMI-backed CPU
clocks were exercised through cpufreq-dt by switching each CPU policy
between its lowest and highest available OPP.

Fixes: ecde921eb460 ("firmware: arm_scmi: Add clock determine_rate operation")
Signed-off-by: Steve Dunnagan <sdunnaga@redhat.com>
Link: https://patch.msgid.link/20260701195923.444270-1-sdunnaga@redhat.com
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

diff --git a/drivers/firmware/arm_scmi/clock.c b/drivers/firmware/arm_scmi/clock.c
index 42e666a628c732e531339df45f1b47b684f3efdc..0278705d809e8ff6b42efd9d966672aeb146d900 100644 (file)
--- a/drivers/firmware/arm_scmi/clock.c
+++ b/drivers/firmware/arm_scmi/clock.c
@@ -718,7 +718,7 @@ static int scmi_clock_rate_set(const struct scmi_protocol_handle *ph,
 static int scmi_clock_determine_rate(const struct scmi_protocol_handle *ph,
                                     u32 clk_id, unsigned long *rate)
 {
-       u64 fmin, fmax, ftmp;
+       u64 fmin, fmax, ftmp, step;
        struct scmi_clock_info *clk;
        struct scmi_clock_desc *clkd;
        struct clock_info *ci = ph->get_priv(ph);
@@ -749,11 +749,14 @@ static int scmi_clock_determine_rate(const struct scmi_protocol_handle *ph,
                return 0;
        }
 
+       step = clkd->r.rates[RATE_STEP];
+       if (!step)
+               return -EINVAL;
+
        ftmp = *rate - fmin;
-       ftmp += clkd->r.rates[RATE_STEP] - 1; /* to round up */
-       ftmp = div64_ul(ftmp, clkd->r.rates[RATE_STEP]);
+       ftmp = DIV64_U64_ROUND_UP(ftmp, step);
 
-       *rate = ftmp * clkd->r.rates[RATE_STEP] + fmin;
+       *rate = ftmp * step + fmin;
 
        return 0;
 }