linux-kernel - Re: [RFC 2/3] mmc: sdhci: add host_ops->voltage

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Date:	Wed, 2 Sep 2015 16:26:27 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
CC:	<linux-mmc@...r.kernel.org>, <ulf.hansson@...aro.org>,
	<linus.walleij@...aro.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 2/3] mmc: sdhci: add host_ops->voltage_switch callback for
 all other voltages

On Wed, 2 Sep 2015 13:49:53 +0530
Vaibhav Hiremath <vaibhav.hiremath@...aro.org> wrote:

> 
> 
> On Wednesday 02 September 2015 12:34 PM, Jisheng Zhang wrote:
> > On Wed, 2 Sep 2015 01:02:17 +0530
> > Vaibhav Hiremath <vaibhav.hiremath@...aro.org> wrote:
> >
> >> Currently, the sdhci_do_start_signal_voltage_switch() function invokes
> >> controller specific voltage switch configuration only for 1.8v usecase;
> >> but it is required for others as well.
> >>
> >> For example, in case of PXA1928 SDH controller, we need to set different
> >> configuration for 3.3, 1.8 and 1.2 volt support (I/O domain power
> >> control register).
> >>
> >> Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
> >> ---
> >> Note:
> >> Currently ->voltage_switch() callback is only supported
> >> in f_sdh30 driver. And I am not sure on the dependency of execution
> >> sequence for that device. I could have moved ->voltage_switch() call
> >> at one common place (above/below), but was not quite sure about it.
> >> So, replicated/duplicated the call for other voltages.
> >>
> >>   drivers/mmc/host/sdhci.c | 8 ++++++++
> >>   1 file changed, 8 insertions(+)
> >>
> >> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> >> index 3dd295f..b59b76d 100644
> >> --- a/drivers/mmc/host/sdhci.c
> >> +++ b/drivers/mmc/host/sdhci.c
> >> @@ -1753,6 +1753,10 @@ static int sdhci_do_start_signal_voltage_switch(struct sdhci_host *host,
> >>   		/* Wait for 5ms */
> >>   		usleep_range(5000, 5500);
> >>
> >> +		/* Some controller need to do more when switching */
> >> +		if (host->ops->voltage_switch)
> >> +			host->ops->voltage_switch(host, MMC_SIGNAL_VOLTAGE_330);
> >
> > Could this be implemented by regulator API? From patch set 3/3, the pxa1928
> > voltage_switch hook is to operate the IO pad registers, this seems not belong
> > to the SDHC IP core.
> >
> 
> Not quite sure whether regulator would be right fit for this.

>From the patche[3/3], this can be achieved by abstracting the IO PAD as regulators
then, we may not need to touch the core sdhci.c. But I'm not sure whether this
is the good solution or not. sdhci Maintainers and experts may have better
suggestions.

> 
> Initially I was thinking of making use of pinconf framework, using
> PIN_CONFIG_POWER_SOURCE, but that too I am not sure is the right way of
> doing it.
> 
> Probably, question for pinctrl maintainer. Looping Linus Walleji.
> 
> Also note that, this configuration is not applicable to all pins/pads,
> only handpicked pads have this configuration (voltage selection on
> pads).
> And this configuration is not part of the same register map.
> 
> It is part of separate register map (AIB_EXT_REG_BASE), called IO
> domain power control register.
> And that
> 
> Thanks,
> Vaibhav

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