[PATCH] mmc: mmci: Improve runtime PM support
Ulf Hansson
ulf.hansson at stericsson.com
Tue Oct 25 03:39:12 EDT 2011
Linus Walleij wrote:
> 2011/10/24 Ulf Hansson <ulf.hansson at stericsson.com>:
>
>> Could we assume that all boards which utilizes the ARM PL180 are using the
>> MMCIPWR register to control power the card? Or should we add a new amba mmci
>> platform member so this is configurable for each board?
>
> I think we should take entire variants, like currently U300 and Ux500.
> In those designs the MMCIPWR signal is left dangling on the chip,
> so no-one electronics designer can use that signal for anything even
> if s/he would have wanted to.
>
>> An option could also be if we might want to simplify code to just skip the
>> entire runtime_suspend|idle|resume function (ie stubb it or something) for
>> these kind of boards?
>
> I think the clk_disable()/clk_enable() pair in runtime suspend/resume
> is still valuable for all other variants too. That has nothing to do with
> MMCIPWR.
>
>> By the way, there is also another option. In the runtime_suspend function
>> for ARM PL180 block we can use mmc_power_save_host (and then also
>> disable vcore etc) and vice verse in runtime_resume with
>> mmc_power_restore_host.
>
> This is what the OMAP driver does right?
Nope.
Right now I think it is only SDIO function drivers through pm_runtime
that can trigger the use of these functions though the bus registered
runtime functions.
>
>> Of course, these kind of operations takes quite some time to execute and
>> therefore we use a much bigger timeout than 50 ms (for example 10 s
>> instead) for ARM PL180.
>
> Can we do both?
That is possible! But I think we need confirmation from Russell first.
Using mmc_power_save_host/mmc_power_restore_host could be a way forward
for ARM PL180, but you should note that initializing a card after it has
been fully powered down, can for really crappy SD-cards take up to 1 s.
Normally this time is 100-400 ms.
This initialization time will then be the latency for the first
read/write after the runtime timeout has expired. There is always a cost
in "performance" when doing power save it seems. :-)
>
> 1) Break out mmci_state_save_restore() from the runtime PM hooks.
>
> 2) I.e. have a short time-out that will runtime-suspend the external
> regulator variants quickly with finer granularity.
>
> 3) Have a long time-out that will runtime-suspend the MMCIPWR
> variants using mmc_power_save_host() with a longer delay?
> Since mmc_power_save_host() calls .set_ios() to really shut
> down the power to the card we should be on the safe side.
>
> Looks like a nice silver bullet to me :-)
>
> I volunteer to test the long time-out code path on the Integrator
> PB1176 to verify this works.
>
> Yours,
> Linus Walleij
>
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