linux-kernel - Re: [PATCH RFC v1 1/3] clk: divider: Add re-usable determine

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Date:   Wed, 19 May 2021 14:31:41 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     mturquette@...libre.com, sboyd@...nel.org,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-clk@...r.kernel.org, khilman@...libre.com,
        linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC v1 1/3] clk: divider: Add re-usable determine_rate
 implementations


On Tue 18 May 2021 at 22:33, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:

> Hi Jerome,
>
> On Tue, May 18, 2021 at 9:44 AM Jerome Brunet <jbrunet@...libre.com> wrote:
> [...]
>> > +int divider_ro_determine_rate(struct clk_hw *hw, struct clk_rate_request *req,
>> > +                           const struct clk_div_table *table, u8 width,
>> > +                           unsigned long flags, unsigned int val)
>> > +{
>> > +     int div;
>> > +
>> > +     div = _get_div(table, val, flags, width);
>> > +
>> > +     /* Even a read-only clock can propagate a rate change */
>> > +     if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
>> > +             if (!req->best_parent_hw)
>> > +                     return -EINVAL;
>> > +
>> > +             req->best_parent_rate = clk_hw_round_rate(req->best_parent_hw,
>> > +                                                       req->rate * div);
>> > +     }
>> > +
>> > +     req->rate = DIV_ROUND_UP_ULL((u64)req->best_parent_rate, div);
>> > +
>> > +     return 0;
>> > +}
>> > +EXPORT_SYMBOL_GPL(divider_ro_determine_rate);
>>
>> For a final version, could you factorize the code with the .round_rate()
>> variant ? It would remove a bit of duplication.
> my first idea was to basically let the new _determine_rate code just
> forward all relevant parameters to _round_rate
> however, I discarded that as it turned out to be less understandable
> for me as parameters need to be mapped in both ways
>
> while writing this mail I noticed that the opposite direction
> (meaning: _round_rate forwards to _determine_rate) will probably work.
> I'll give it a try in the next days
> if you had anything else in mind then please let me know

Yep, the idea would be to use the determine_rate() part as the common
implementation. AFAICT, all you need is to build req_rate structure in
the round_rate() part.

>
>> Maybe determine_rate() can also replace round_rate() in the generic
>> divider ops ?
> sure, I'll add that as a separate patch in this series
> note to myself: testing can be done with the MMC drivers as we're
> using the generic clk_divider_ops there
>
>
> Best regards,
> Martin