linux-kernel - Re: [PATCH v9 5/6] clk: Add floor and ceiling constraints to clock rates

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Message-ID: <54082871.8080808@collabora.com>
Date:	Thu, 04 Sep 2014 10:53:05 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	linux-kernel@...r.kernel.org, tomasz.figa@...il.com, rabin@....in,
	Thierry Reding <thierry.reding@...il.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 5/6] clk: Add floor and ceiling constraints to clock
 rates

On 09/04/2014 02:53 AM, Mike Turquette wrote:
> Quoting Stephen Boyd (2014-09-03 16:39:37)
>> On 09/03/14 08:33, Tomeu Vizoso wrote:
>>> +int clk_set_ceiling_rate(struct clk *clk_user, unsigned long rate)
>>> +{
>>> +     struct clk_core *clk = clk_to_clk_core(clk_user);
>>> +
>>> +     WARN(rate > 0 && rate < clk_user->floor_constraint,
>>> +          "clk %s dev %s con %s: new ceiling %lu lower than existing floor %lu\n",
>>> +          __clk_get_name(clk), clk_user->dev_id, clk_user->con_id, rate,
>>> +          clk_user->floor_constraint);
>>> +
>>> +     clk_user->ceiling_constraint = rate;
>>> +     return clk_provider_set_rate(clk, clk_provider_get_rate(clk));
>>> +}
>>> +EXPORT_SYMBOL_GPL(clk_set_ceiling_rate);
>>
>> Maybe I'm late to this patch series given that Mike applied it, but I
>> wonder why we wouldn't just have one API that takes a min and a max,
>> i.e. clk_set_rate_range(clk, min, max)? Then clk_set_rate() is a small
>> wrapper on top that just sets min and max to the same value.
> 
> We certainly can have that. But being able to easily adjust a floor or
> ceiling value seems like a good thing to me, and that is what these
> functions do.
> 
> If we decide to have a clk_set_rate_range (where we perhaps pass zero in
> for a value that we do not wish to constrain) then I imagine that
> clk_set_ceiling_rate and clk_set_floor_rate will simply become a wrapper
> for that function. No harm having it both ways. If one way of doing
> things falls out of favor we can always cull it and update all the
> users.

I opted for separate functions because in the specific use cases I
thought of, any user will be interested in setting either a floor or a
ceiling constraint, but not both.

Regards,

Tomeu
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