linux-kernel - Re: [PATCH 3/3 RESEND] mmc: sdhci: check voltage range only on regulators aware of voltage value

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Date:	Wed, 13 Feb 2013 08:45:56 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
cc:	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Chris Ball <cjb@...top.org>,
	Kevin Liu <keyuan.liu@...il.com>
Subject: Re: [PATCH 3/3 RESEND] mmc: sdhci: check voltage range only on
 regulators aware of voltage value

On Wed, 13 Feb 2013, Marek Szyprowski wrote:

> Hello,
> 
> On 2/12/2013 11:10 PM, Guennadi Liakhovetski wrote:
> > Hi Marek
> > 
> > On Tue, 12 Feb 2013, Marek Szyprowski wrote:
> > 
> > > Some regulators don't report any voltage values, so checking supported
> > > voltage range results in disabling all SDHCI_CAN_VDD_* flags and
> > > registration failure. This patch finally provides a correct fix for the
> > > registration of SDHCI driver with all possible voltage regulators:
> > > dummy, fixed and regulated without using regulator_count_voltages()
> > > hacks.
> > >
> > > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > > ---
> > >  drivers/mmc/host/sdhci.c |    6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > > index ba586ae..735526b 100644
> > > --- a/drivers/mmc/host/sdhci.c
> > > +++ b/drivers/mmc/host/sdhci.c
> > > @@ -2976,7 +2976,11 @@ int sdhci_add_host(struct sdhci_host *host)
> > >  	}
> > >
> > >  #ifdef CONFIG_REGULATOR
> > > -	if (host->vmmc) {
> > > +	/*
> > > +	 * Voltage range check makes sense only if regulator reports
> > > +	 * any voltage value.
> > > +	 */
> > > +	if (host->vmmc && regulator_get_voltage(host->vmmc) > 0) {
> > >  		ret = regulator_is_supported_voltage(host->vmmc, 2700000,
> > >  			3600000);
> > 
> > Wouldn't using mmc_regulator_get_ocrmask() be a better option?
> 
> The idea behind this patch it to avoid messing ocr mask and voltage
> regulators when voltage regulator is a simple on/off switch, which doesn't
> report any value.

Wouldn't mmc_regulator_get_ocrmask() also report an error back in this 
case?

> This solves the serious problems with sdhci driver when
> dummy regulator is enabled in kconfig, otherwise the sdhci driver
> concludes that no supported voltage is available and fails to initialize.
> Using mmc_regulator_get_ocrmask() won't solve this problem.
> 
> BTW, mmc_regulator_get_ocrmask() won't work with continuous range regulators.

This seems like a problem, that has to be fixed...

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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