Re: [PATCH 0/2] clk: Implement a clock request API

[Maxime Ripard <maxime@cerno.tech>]

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Hi Stephen,

On Fri, Apr 30, 2021 at 01:59:39PM -0700, Stephen Boyd wrote:
> Quoting Maxime Ripard (2021-04-13 03:13:18)
> > Hi,
> > 
> > This is a follow-up of the discussion here:
> > https://lore.kernel.org/linux-clk/20210319150355.xzw7ikwdaga2dwhv@gilmour/
> > 
> > This implements a mechanism to raise and lower clock rates based on consumer
> > workloads, with an example of such an implementation for the RaspberryPi4 HDMI
> > controller.
> > 
> > There's a couple of things worth discussing:
> > 
> >   - The name is in conflict with clk_request_rate, and even though it feels
> >     like the right name to me, we should probably avoid any confusion
> > 
> >   - The code so far implements a policy of always going for the lowest rate
> >     possible. While we don't have an use-case for something else, this should
> >     maybe be made more flexible?
> 
> I'm definitely confused how it is different from the
> clk_set_rate_exclusive() API and associated
> clk_rate_exclusive_get()/clk_rate_exclusive_put(). Can you explain
> further the differences in the cover letter here?

The exclusive API is meant to prevent the clock rate from changing,
allowing a single user to make sure that no other user will be able to
change it.

What we want here is instead to allow multiple users to be able to
express a set of minimum rates and then let the CCF figure out a rate
for that clock that matches those constraints (so basically what
clk_set_min_rate does), but then does allow for the clock to go back to
its initial rate once that constraint is not needed anymore.

So I guess it's more akin to clk_set_min_rate with rollback than the
exclusive API?

Maxime

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