linux-kernel - Re: [PATCH 05/17] mmc: mmci: Put the device into low power state at system suspend

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Date:	Mon, 10 Feb 2014 12:11:24 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Kevin Hilman <khilman@...aro.org>
Cc:	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Alessandro Rubini <rubini@...pv.it>,
	Linus Walleij <linus.walleij@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Chris Ball <chris@...ntf.net>, Mark Brown <broonie@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH 05/17] mmc: mmci: Put the device into low power state at
 system suspend

On 4 February 2014 20:22, Kevin Hilman <khilman@...aro.org> wrote:
> Ulf Hansson <ulf.hansson@...aro.org> writes:
>
>> Due to the available runtime PM callbacks, we are now able to put our
>> device into low power state at system suspend.
>>
>> Earlier we could not accomplish this without trusting a power domain
>> for the device to take care of it. Now we are able to cope with
>> scenarios both with and without a power domain.
>>
>> Cc: Russell King <linux@....linux.org.uk>
>> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
>> ---
>>  drivers/mmc/host/mmci.c |   45 +++++++++++++++++++++++++--------------------
>>  1 file changed, 25 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
>> index c88da1c..074e0cb 100644
>> --- a/drivers/mmc/host/mmci.c
>> +++ b/drivers/mmc/host/mmci.c
>> @@ -1723,33 +1723,38 @@ static int mmci_remove(struct amba_device *dev)
>>       return 0;
>>  }
>>
>> -#ifdef CONFIG_SUSPEND
>> -static int mmci_suspend(struct device *dev)
>> +#ifdef CONFIG_PM_SLEEP
>> +static int mmci_suspend_late(struct device *dev)
>>  {
>> -     struct amba_device *adev = to_amba_device(dev);
>> -     struct mmc_host *mmc = amba_get_drvdata(adev);
>> +     int ret = 0;
>>
>> -     if (mmc) {
>> -             struct mmci_host *host = mmc_priv(mmc);
>> -             pm_runtime_get_sync(dev);
>> -             writel(0, host->base + MMCIMASK0);
>> -     }
>> +     if (pm_runtime_status_suspended(dev))
>> +             return 0;
>>
>> -     return 0;
>> +     if (dev->pm_domain && dev->pm_domain->ops.runtime_suspend)
>> +             ret = dev->pm_domain->ops.runtime_suspend(dev);
>> +     else
>> +             ret = dev->bus->pm->runtime_suspend(dev);
>> +
>> +     if (!ret)
>> +             pm_runtime_set_suspended(dev);
>
> Isn't this basically open-coding pm_runtime_suspend()...

It is similar, but with once big difference.

Since the PM core prevents pm_runtime_suspend() from invoking our
->runtime_suspend callback during system suspend (it does so by
invoking pm_runtime_get_sync() before starting the suspend sequence),
we then need to make the driver handle that by itself.

>
>> +     return ret;
>>  }
>>
>> -static int mmci_resume(struct device *dev)
>> +static int mmci_resume_early(struct device *dev)
>>  {
>> -     struct amba_device *adev = to_amba_device(dev);
>> -     struct mmc_host *mmc = amba_get_drvdata(adev);
>> +     int ret = 0;
>>
>> -     if (mmc) {
>> -             struct mmci_host *host = mmc_priv(mmc);
>> -             writel(MCI_IRQENABLE, host->base + MMCIMASK0);
>> -             pm_runtime_put(dev);
>> -     }
>> +     if (pm_runtime_status_suspended(dev))
>> +             return 0;
>>
>> -     return 0;
>> +     if (dev->pm_domain && dev->pm_domain->ops.runtime_resume)
>> +             ret = dev->pm_domain->ops.runtime_resume(dev);
>> +     else
>> +             ret = dev->bus->pm->runtime_resume(dev);
>> +
>> +     return ret;
>
> ...and this is pm_runtime_resume()? (though both terribly simplified.)

Correct, but again with a big difference. See comment above.

>
> This is starting to show that building with PM_SLEEP but not PM_RUNTIME
> is going to force open-coding a lot of stuff that the runtime PM
> framework already provides.  So either we need some helper functions so
> we're not sprinkling manual calls to bus/pm_domain callbacks all over

I have send a patch a while ago for the PM core, that tried to
implement something similar like this, I wasn't accepted. I will
follow up on that asap.

Still, do you think we could go ahead with this patch? If/when we can
get an acceptance for a PM runtime helper function in the PM core, we
can easily convert to use it later on.

> the place, or maybe where we need to go is have a way for platforms that
> really are "runtime PM centric" to declare that even PM_SLEEP depends on
> PM_RUNTIME.
>
> I'm trying to thing of a good reason to not make PM_SLEEP depend on
> PM_RUNTIME for platforms like this.

This wont help. The PM core will still prevent the runtime_suspend
callback from being invoked during system suspend.


Kind regards
Ulf Hansson

>
> Kevin
>
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