[PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Arnd Hannemann]

On some boards card power is hard wired to the slot
and active regardless of host controller state.
When runtime PM suspends such a host, certain cards
may keep their current configuration (e.g. bus width),
now when runtime PM resumes the host, communication
with the card will fail.
This was observed on AP4EVB with tmio_mmc and a b43 based
SDIO card:
http://marc.info/?l=linux-mmc&m=128854536521274&w=2

This patch, fixes the problem by resetting the SDIO
card on power restore.

Signed-off-by: Arnd Hannemann <arnd@arndnet.de>
---
 drivers/mmc/core/core.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 31ae07a..21cdee6 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1617,8 +1617,13 @@ int mmc_power_restore_host(struct mmc_host *host)
 	}
 
 	mmc_power_up(host);
-	ret = host->bus_ops->power_restore(host);
 
+	mmc_claim_host(host);
+	sdio_reset(host);
+	mmc_go_idle(host);
+	mmc_release_host(host);
+
+	ret = host->bus_ops->power_restore(host);
 	mmc_bus_put(host);
 
 	return ret;
-- 
1.7.2.3

Re: [PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Ohad Ben-Cohen]

On Tue, Dec 28, 2010 at 1:25 PM, Arnd Hannemann <arnd@arndnet.de> wrote:
> On some boards card power is hard wired to the slot
> and active regardless of host controller state.
...
> This was observed on AP4EVB with tmio_mmc and a b43 based
> SDIO card:
> http://marc.info/?l=linux-mmc&m=128854536521274&w=2

Do you mean that your card is always powered on regardless of
mmc_power_off() invocations ?

I always wondered why SDIO runtime PM didn't work with your card, so
thanks for the follow up on this.

That said, if you card can't be powered down, then it shouldn't be
MMC_CAP_POWER_OFF_CARD at all (which literally means that the card can
be powered down).

And if it isn't MMC_CAP_POWER_OFF_CARD, then runtime PM will stay
disabled for the card, so the problem you describe can't happen.

Thanks,
Ohad.

Re: [PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Arnd Hannemann]

Hi Ohad,

Am 28.12.2010 13:45, schrieb Ohad Ben-Cohen:
> On Tue, Dec 28, 2010 at 1:25 PM, Arnd Hannemann <arnd@arndnet.de> wrote:
>> On some boards card power is hard wired to the slot
>> and active regardless of host controller state.
> ...
>> This was observed on AP4EVB with tmio_mmc and a b43 based
>> SDIO card:
>> http://marc.info/?l=linux-mmc&m=128854536521274&w=2
> 
> Do you mean that your card is always powered on regardless of
> mmc_power_off() invocations ?

Yes, it seems so.

> I always wondered why SDIO runtime PM didn't work with your card, so
> thanks for the follow up on this.
> 
> That said, if you card can't be powered down, then it shouldn't be
> MMC_CAP_POWER_OFF_CARD at all (which literally means that the card can
> be powered down).
> 
> And if it isn't MMC_CAP_POWER_OFF_CARD, then runtime PM will stay
> disabled for the card, so the problem you describe can't happen.

Even if the card is kept powered, when mmc_power_off() is called, the
host controller will stop the SD bus clock. So I believe at least some
power is saved this way and MMC_CAP_POWER_OFF_CARD makes sense?

Thanks,
Arnd

Re: [PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Ohad Ben-Cohen]

Hi Arnd,

On Tue, Dec 28, 2010 at 4:03 PM, Arnd Hannemann <arnd@arndnet.de> wrote:
>> Do you mean that your card is always powered on regardless of
>> mmc_power_off() invocations ?
>
> Yes, it seems so.

Ok, thanks for letting us know.

It bothered me that we didn't understand the issue you had, but now it
seems that MMC_CAP_POWER_OFF_CARD is the right solution for you as
well.

> Even if the card is kept powered, when mmc_power_off() is called, the
> host controller will stop the SD bus clock. So I believe at least some
> power is saved this way and MMC_CAP_POWER_OFF_CARD makes sense?

Well, with some SDIO cards, the host controller can use the recently
added aggressive clock gating framework to stop the clock on
inactivity, and not wait until the card is powered off.

Currently that clock gating framework is still disabled for SDIO
cards, but this is just temporary until we sort out how to use it
safely for SDIO as well.

For example, the wl1271 card has asynchronous interrupts (via external
irq) so we can safely stop its clock on inactivity.

Do you know if that's possible with your card as well ?

Thanks,
Ohad.

Re: [PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Arnd Hannemann]

Hi Ohad,

Am 28.12.2010 15:24, schrieb Ohad Ben-Cohen:
>>> Do you mean that your card is always powered on regardless of
>>> mmc_power_off() invocations ?
>>
>> Yes, it seems so.
> 
> Ok, thanks for letting us know.
> 
> It bothered me that we didn't understand the issue you had, but now it
> seems that MMC_CAP_POWER_OFF_CARD is the right solution for you as
> well.
> 
>> Even if the card is kept powered, when mmc_power_off() is called, the
>> host controller will stop the SD bus clock. So I believe at least some
>> power is saved this way and MMC_CAP_POWER_OFF_CARD makes sense?
> 
> Well, with some SDIO cards, the host controller can use the recently
> added aggressive clock gating framework to stop the clock on
> inactivity, and not wait until the card is powered off.
> 
> Currently that clock gating framework is still disabled for SDIO
> cards, but this is just temporary until we sort out how to use it
> safely for SDIO as well.

So you suggest to don't set MMC_CAP_POWER_OFF_CARD for the boards which
keep the card powered, but instead wait for the clock gating framework?
 
> For example, the wl1271 card has asynchronous interrupts (via external
> irq) so we can safely stop its clock on inactivity.
> 
> Do you know if that's possible with your card as well ?

I don't think so, the card is a normal SDIO card which plugs into a normal
MMC/SD slot, no extra pins or such. However SDIO IRQs are available, but you
don't mean that, do you?

Thanks,
Arnd

Re: [PATCH] [RFC] mmc: perform SDIO reset on power restore of host

[Ohad Ben-Cohen]

Hi Arnd,

On Wed, Dec 29, 2010 at 12:35 PM, Arnd Hannemann <arnd@arndnet.de> wrote:
> So you suggest to don't set MMC_CAP_POWER_OFF_CARD for the boards which
> keep the card powered

Yes, if you can't power off your card, it doesn't make a lot of sense
to set it MMC_CAP_POWER_OFF_CARD.

If the reason is to notify the host controller, via runtime PM, to
disable the clock to the card, we need first to see that it works
(have you tested it ? how ?): currently there are no host controllers
which employ runtime PM. It looks like sdhci is about to, but it is
still not clear how exactly - it is just being discussed.

Moreover, it seems that host controllers will ignore the card's
runtime PM status, in order to allow them to independently manage
their runtime PM status (and by that disable clocks more
aggressively).

So I'd wait to see how those discussions evolve (or jump in and have
my use case considered) but before that it won't make a lot of sense
to add MMC_CAP_POWER_OFF_CARD for cards that are always powered on,
because it is currently still not clear that it will yield any
benefit.

>> For example, the wl1271 card has asynchronous interrupts (via external
>> irq) so we can safely stop its clock on inactivity.
>>
>> Do you know if that's possible with your card as well ?
>
> I don't think so, the card is a normal SDIO card which plugs into a normal
> MMC/SD slot, no extra pins or such. However SDIO IRQs are available, but you
> don't mean that, do you?

Some cards do support asynchronous SDIO IRQs (do you know if yours too
btw ?). How this is going to be safely employed is still in
discussions...

Thanks,
Ohad.