linux-kernel - Re: [PATCH v3 2/3] clk: divider: Switch from .round_rate to .determine

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Date:   Fri, 2 Jul 2021 14:46:11 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, mturquette@...libre.com,
        linux-clk@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>, jbrunet@...libre.com,
        khilman@...libre.com, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/3] clk: divider: Switch from .round_rate to
 .determine_rate by default

Hi

On 02.07.2021 11:19, Martin Blumenstingl wrote:
> Hi Stephen,
>
> On Fri, Jul 2, 2021 at 3:02 AM Stephen Boyd <sboyd@...nel.org> wrote:
> [...]
>> My guess is that we have drivers copying the clk_ops from the
>> divider_ops structure and so they are copying over round_rate but not
>> determine_rate.
> I just learned something new - thanks for investigating this as well!
>
> $ git grep "clk_divider_ops\.round_rate" drivers/
> drivers/clk/bcm/clk-bcm2835.c:  return clk_divider_ops.round_rate(hw,
> rate, parent_rate);

I confirm that this issue appears also on Raspberry Pi 3b+ board. I was 
about to write a bug report, but you were faster. The funny thing is 
that is so nondeterministic, that automated bisecting failed to catch it.

> drivers/clk/clk-stm32f4.c:      return clk_divider_ops.round_rate(hw,
> rate, prate);
> drivers/clk/clk-stm32h7.c:      return clk_divider_ops.round_rate(hw,
> rate, prate);
> drivers/clk/clk-stm32mp1.c:             req->rate =
> clk_divider_ops.round_rate(hw, req->rate, &best_parent_rate);
> drivers/clk/imx/clk-divider-gate.c:     return
> clk_divider_ops.round_rate(hw, rate, prate);
> $ git grep "clk_divider_ro_ops\.round_rate" drivers/
> $
>
> Changing these over to use clk_divider_ops.determine_rate doesn't seem too hard.
> The part that I am not sure about is how to organize the patches.
> 1) amend the changes to all relevant drivers (from above) to this patch
> 2) multiple patches:
> - adding .determine_rate to the default divider ops (but not removing
> .round_rate)
> - a single patch for each relevant driver (from above)
> - removing .round_rate from the default divider ops
>
> Another approach is to first create clk_divider_determine_rate() (as
> done here) and export it.
> Then I could have one individual patch for each relevant driver (from
> above) to use:
>    .determine_rate = clk_divider_determine_rate,
> Then finally I could remove clk_divider_round_rate() and switch over
> the default divider ops to .determine_rate as well.
>
> Which way do you prefer?
>
>
> Best regards,
> Martin
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland