Re: [PATCH] mmc: mmci: Improve runtime PM support

[Ulf Hansson <ulf.hansson@xxxxxxxxxxxxxx>]

Russell King - ARM Linux wrote:
> On Mon, Oct 24, 2011 at 11:54:00AM +0200, Linus Walleij wrote:
> > On Mon, Oct 24, 2011 at 11:36 AM, Russell King - ARM Linux
> > <linux@xxxxxxxxxxxxxxxx> wrote:
> > > On Sun, Oct 23, 2011 at 02:31:39AM +0200, Sebastian Rasmussen wrote:
> > > > I guess the patch would appeal more to Russell if mmci_runtime_suspend()
> > > > only cleared MCIMask0/SDI_MASK0 and MCIClock/SDI_CLKCR and left
> > > > MCIPower/SDI_PWR unchanged. It may be the case that the signal direction
> > > > bits need to be cleared for the ST-Ericsson PL180, but I haven't yet verified
> > > > this on my Snowball dev board yet.
> > > There's also the issue that the specs call for the clock to run after
> > > a command has completed for a certain number of cycles, and that the
> > > clock must continue to run until the card reports not-busy after a
> > > programming or erase cycle has completed - that can be long after the
> > > previous command has 'completed'.
> > It's 8 cycles on MCLK required.
>
> _Plus_ keeping the clock running while the card is signalling busy.
>
> If you don't clock the card while its signalling busy, it will never
> go non-busy (the data line becomes frozen.)

Good point!

Is the aggressive clk gating feature in the mmc framework taking this 
into account as well?

Potentially the framework could do a get_sync/put (in claim/release 
host) to prevent hosts from being runtime disabled. Similar how the 
enable/disable mechanism is working.


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel