[PATCH] mmc: mmci: Improve runtime PM support

[ulf.hansson@stericsson.com (Ulf Hansson)]

Linus Walleij wrote:
> On Mon, Oct 24, 2011 at 1:48 PM, Ulf Hansson <ulf.hansson@stericsson.com> wrote:
>> [Russell]
>>> The MCIPWR signal controls the external power switch.  This is the only
>>> signal for it.  This is the only connection for it.  There is no other
>>> control form for this power switch.
>>>
>> Then we are only left to use the variant struct I believe. In principle, a
>> flag in the variant struct, could indicate whether it is OK to disable the
>> vcore regulator and thus clear the MCIPWR when doing runtime_suspend.
> 
> Yep I think the best could be to add some variant named
> bool external_card_power; and then document in the kerneldoc that this
> means the driver can clear MMCIPWR without risk of cutting the power
> to the card.
> 
> This should be true for Ux500, U300 and Nomadik (just checked the designs -
> they all have external regulators).
> 

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?

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?

What do you prefer?

> So the state save/restore and amba_vcore_disable(adev); should be done
> only for those variants.
> 
> However this:
> 
> clk_disable(host->clk);
> 
> We ought to be able to do for *all* variants, provided we can create
> pm_runtime_get/put and delay properly to cover all bus traffic
> (looks like the patch already does that), plus all the time the card is
> signalling busy. The best I can think of is to just return -EBUSY to runtime
> PM like this:
> 
> if ((readl(base + MMCISTATUS) & (MCI_CMDACTIVE | MCI_TXACTIVE| MCI_RXACTIVE))
>   return -EBUSY;
> 
> Yours,
> Linus Walleij
>