Clock API and "maximum rate"

[Matt Sealey]

On Thu, Jan 12, 2012 at 8:11 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Thu, Jan 12, 2012 at 07:49:35AM -0600, Matt Sealey wrote:
>> On Wed, Jan 11, 2012 at 10:58 AM, Jamie Iles <jamie at jamieiles.com> wrote:
>> > Hi Matt,
>> >
>> > On Wed, Jan 11, 2012 at 10:30:15AM -0600, Matt Sealey wrote:
>> >> Just a curious question, is there any safe way in the current API or
>> >> even by peeking a little behind the scenes to find out what the
>> >> maximum clock rate would be for a given named clock or struct clk?
>> >
>> > How about:
>> >
>> >        long max = clk_round_rate(clk, ~0LU);
>> >
>> > clk_round_rate() is one of the optional API calls though.
>>
>> Luckily implemented in this case :) Seems to do the trick, thanks.
>
> If it's not implemented, but there is an implemented clk_set_rate(), feel
> free to complain at whoever created the implementation.
>
> If there's a clk_set_rate() implementation, then there's _already_ an
> implementation of clk_round_rate() internally doing the rounding for the
> set_rate function, so there's really no excuse not to expose that via
> clk_round_rate().
>
> clk_round_rate() is supposed to tell you what you end up with if you
> ask clk_set_rate() to set the exact same value you passed in - but
> clk_round_rate() won't modify the hardware.
>
> So, clk_round_rate/clk_set_rate really should be thought of being
> implemented as this:
>
> long clk_round_rate(struct clk *clk, unsigned long rate)
> {
>        return __clk_round_rate(clk, rate);
> }
>
> int clk_set_rate(struct clk *clk, unsigned long rate)
> {
>        long rate = __clk_round_rate(clk, rate);
>
>        if (rate < 0)
>                return rate;
>
>        return __clk_set_rate(clk, rate);
> }

Right. On i.MX it seems not to round first, but to assume you passed a
rounded rate? I assume the upper level clk API does the above, so the
low level doesn't have to?

-- 
Matt Sealey <matt at genesi-usa.com>
Product Development Analyst, Genesi USA, Inc.