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