linux-kernel - Re: [PATCH v2 2/2] spi: amlogic-spifc-a1: add support for max_speed

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Message-ID: <45116f61-6ee7-919c-7c99-704a5b274df8@sberdevices.ru>
Date:   Mon, 24 Jul 2023 18:15:14 +0300
From:   Martin Kurbanov <mmkurbanov@...rdevices.ru>
To:     Mark Brown <broonie@...nel.org>
CC:     Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        <linux-spi@...r.kernel.org>, <linux-amlogic@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kernel@...rdevices.ru>
Subject: Re: [PATCH v2 2/2] spi: amlogic-spifc-a1: add support for
 max_speed_hz



On 20.07.2023 18:46, Mark Brown wrote:
> On Thu, Jul 20, 2023 at 06:41:11PM +0300, Martin Kurbanov wrote:
>> On 11.07.2023 10:25, Jerome Brunet wrote:
> 
>>>> +	ret = clk_set_rate(spifc->clk, freq);
>>>> +	if (ret)
>>>> +		return ret;
> 
>>>> +	spifc->curr_speed_hz = freq;
> 
>>> There is no guarantee that clk_set_rate() has set the rate you have
>>> requested, at least not precisely. You should call clk_get_rate() here.
> 
>> Are you referring to a situation where there is a change in the rate due
>> to a request from another client, such as a sibling driver with the same
>> parent clock?
> 
> The clock may simply not be able to generate exactly the rate you
> requested, the rate will be rounded to some value that the clock can
> actually generate.

Yes, I understand the situation. However, I am comparing it with the
requested frequency rather than the actual one that has been set.
Therefore, I asked Jerome for clarification regarding whether the
frequency can be changed by another client (driver). Maybe, it's better
to remove this condition at all? CCF has a cached rate value and doesn't
run 'set' operation if it's not needed.

-- 
Best Regards,
Martin Kurbanov