Re: [RFC PATCH 1/4] memory: tegra124-emc: Add EMC driver

[Tomeu Vizoso]

On 06/17/2014 06:15 PM, Stephen Warren wrote:
> On 06/17/2014 06:16 AM, Tomeu Vizoso wrote:
> > On 06/16/2014 10:02 PM, Stephen Warren wrote:
> > > On 06/16/2014 07:35 AM, Tomeu Vizoso wrote:
> > > > +#ifdef CONFIG_TEGRA124_EMC
> > > > +int tegra124_emc_reserve_bandwidth(unsigned int consumer, unsigned
> > > > long rate);
> > > > +void tegra124_emc_set_floor(unsigned long freq);
> > > > +void tegra124_emc_set_ceiling(unsigned long freq);
> > > > +#else
> > > > +int tegra124_emc_reserve_bandwidth(unsigned int consumer, unsigned
> > > > long rate)
> > > > +{ return -ENODEV; }
> > > > +void tegra124_emc_set_floor(unsigned long freq)
> > > > +{ return; }
> > > > +void tegra124_emc_set_ceiling(unsigned long freq)
> > > > +{ return; }
> > > > +#endif
> > >
> > > I'll repeat what I said off-list so that we can have the whole
> > > conversation on the list:
> > >
> > > That looks like a custom Tegra-specific API. I think it'd be much better
> > > to integrate this into the common clock framework as a standard clock
> > > constraints API. There are other use-cases for clock constraints besides
> > > EMC scaling (e.g. some in audio on Tegra, and I'm sure many on other
> > > SoCs too).
> >
> > Yes, I wrote a bit in the cover letter about our requirements and how
> > they map to the CCF. Could you please comment on that?
>
> My comments remain the same. I believe this is something that belongs in
> the clock driver, or at the least, some API that takes a struct clock as
> its parameter, so that drivers can use the existing DT clock lookup
> mechanism.

Ok, let me put this strawman here to see if I have gotten close to what 
you have in mind:

* add per-client accounting (Rabin's patches referenced before)

* add clk_set_floor, to be used by cpufreq, load stats, etc.

* add clk_set_ceiling, to be used by battery drivers, thermal, etc.

* an EMC driver would collect bandwidth and latency requests from 
consumers and call clk_set_floor on the EMC clock.

* the EMC driver would also register for rate change notifications in 
the EMC clock and would update the latency allowance registers at that 
point.

How does it sound?

Regards,

Tomeu
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