linux-kernel - Re: [PATCH v4 05/11] clk: Introduce clk-tps68470 driver

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Message-ID: <4aec04d1-0964-e4c3-2c92-f9cef395494a@redhat.com>
Date:   Mon, 1 Nov 2021 12:00:49 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Daniel Scally <djrscally@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Kate Hsuan <hpa@...hat.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v4 05/11] clk: Introduce clk-tps68470 driver

Hi,

On 11/1/21 11:42, Andy Shevchenko wrote:
> On Mon, Nov 1, 2021 at 12:27 PM Hans de Goede <hdegoede@...hat.com> wrote:
>> On 10/25/21 13:24, Andy Shevchenko wrote:
>>> On Mon, Oct 25, 2021 at 12:42 PM Hans de Goede <hdegoede@...hat.com> wrote:
> 
> ...
> 
>>>> +       for (i = 0; i < ARRAY_SIZE(clk_freqs); i++) {
>>>> +               diff = clk_freqs[i].freq - rate;
>>>> +               if (diff == 0)
>>>> +                       return i;
>>>
>>>> +               diff = abs(diff);
>>>
>>> This needs a comment why higher (lower) frequency is okay.
>>
>> This function is called in 2 places:
>>
>> 1. From tps68470_clk_round_rate(), where higher/lower clearly is ok,
>> (see the function name) so no comment needed.
>>
>> 2. From tps68470_clk_set_rate() where it is NOT ok and this is
>> enforced in the caller:
>>
>>         unsigned int idx = tps68470_clk_cfg_lookup(rate);
>>
>>         if (rate != clk_freqs[idx].freq)
>>                 return -EINVAL;
>>
>> This is not easy to describe in a comment, while being obvious
>> if someone looking at this actually looks at the callers.
> 
> Hmm... but try your best. :-)

Ok I will :)

> While at it, recently I have learned about util_macros.h. Any use of it here?
> Or amending it there and re-using it here?

That only works on straight integer/long/float arrays, not
on arrays of structs where we are looking for a specific member of
the struct to be closest. And reworking that to also work on
structs is really (really really) out of scope for this patch-set.

Regards,

Hans


> 
>>>> +               if (diff < best_diff) {
>>>> +                       best_diff = diff;
>>>> +                       best_idx = i;
>>>> +               }
>>>> +       }
>