Re: [PATCH v2 0/9] soc: qcom: geni: Derive SE clock configuration from OPP table on SA8255P

[Praveen Talari <praveen.talari@oss.qualcomm.com>]

Hi Konrad,

On 04-09-2026 14:30, Konrad Dybcio wrote:
> On 9/4/26 9:56 AM, Ulf Hansson wrote:
>> On Tue, Sep 1, 2026 at 6:48 PM Praveen Talari
>> <praveen.talari@oss.qualcomm.com> wrote:
> [...]
>
>> So geni_se_clk_freq_match() is used by two consumer drivers today,
>> drivers/spi/spi-geni-qcom.c and drivers/tty/serial/qcom_geni_serial.c.
>>
>> Beyond the $subject series, there will be even more consumer drivers
>> that call these platform specific functions. As I said above, I don't
>> think this is moving things in the right direction.
>>
>> If this can't be solved with generic frameworks (clocks and OPP),
>> please clarify why so we can figure out a better way forward.
> The way I read it, isn't geni_se_clk_freq_match() more or less
> dev_pm_opp_find_freq_exact() called in a loop with an increasing
> divider?
Currently, geni_se_clk_freq_match() relies on clk_perf_tbl to
determine the source clock index and divider corresponding to
a requested frequency.

On Linux-managed platforms, clk_perf_tbl is populated by
geni_se_clk_tbl_get(), which enumerates the supported source
clock frequencies using clk_round_rate().

int geni_se_clk_freq_match(struct geni_se *se, unsigned long req_freq,
                unsigned int *index, unsigned long *res_freq,
                bool exact)
{
     [...]

     num_clk_levels = geni_se_clk_tbl_get(se, &tbl);
     if (num_clk_levels < 0)
         return num_clk_levels;
     [...]
     best_delta = ULONG_MAX;
     for (i = 0; i < num_clk_levels; i++) {
         divider = DIV_ROUND_UP(tbl[i], req_freq);
         new_delta = req_freq - tbl[i] / divider;
         if (new_delta < best_delta) {
             /* We have a new best! */
             *index = i;
             *res_freq = tbl[i];

             /* If the new best is exact then we're done */
             if (new_delta == 0)
                 return 0;

             /* Record how close we got */
             best_delta = new_delta;
         }
     }

[...]

     return 0;
}

On firmware-managed platforms, clk_perf_tbl is populated from
the performance-domain OPP table during domain attachment,
allowing geni_se_clk_freq_match() to operate on the same source
clock frequency information irrespective of how the underlying
resources are managed.

As a result, the frequency matching logic, including source
clock selection and divider calculation, remains common across
both Linux-managed and firmware-managed configurations, while
only the mechanism used to apply the selected rate differs.

Thanks,

Praveen Talari

>
> Konrad