[PATCH] mmc: dw_mmc: Turn the card clock off at suspend time
abrestic at chromium.org
Wed Nov 19 11:49:32 PST 2014
On Wed, Nov 19, 2014 at 11:30 AM, Doug Anderson <dianders at chromium.org> wrote:
> On Wed, Nov 19, 2014 at 11:03 AM, Andrew Bresticker
> <abrestic at chromium.org> wrote:
>> On Wed, Nov 19, 2014 at 10:51 AM, Doug Anderson <dianders at chromium.org> wrote:
>>> Since the dw_mmc driver was first added to Linux it's had a TODO in it
>>> that we should turn off the card clock during suspend. I have no idea
>>> for sure why it wasn't done originally, but if I had to guess I'd
>>> guess it was related to the lack of a common clock framework. Let's
>>> do it now.
>>> There is no reason for the card clock to be left on during suspend and
>>> most systems will eventually turn it off anyway (when whole clock
>>> trees are disabled). However, it's good to be explicit that it's
>>> disabled at the time that the MMC subsystem is disabled.
>> Should the bus clock (biu) be disabled as well?
> Good question. I'm slightly hesitant to turn biu_clk off in this
> patch, though. Specifically interrupts are still enabled at this
> point in suspend. I guess most interrupts shouldn't be going off
> right now (nobody is accessing storage, right?), but I could imagine
> that a card detect or an SDIO interrupt at just the wrong time could
> cause our ISR to go off _after_ this function is called. The
> interrupt handling function doesn't know to turn the BIU clock back on
> so you'd get a hang.
Perhaps interrupts should be disabled as well across suspend/resume,
like the sdhci-based hosts do? Would would happen if we tried to
service an interrupt with the ciu clock disabled?
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