linux-kernel - Re: [RFC PATCH v3.1 14/27] mmc: sdhci-uhs2: skip signal_voltage

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Message-ID: <20201130073805.GE48535@laputa>
Date:   Mon, 30 Nov 2020 16:38:05 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     ulf.hansson@...aro.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, ben.chuang@...esyslogic.com.tw,
        greg.tu@...esyslogic.com.tw
Subject: Re: [RFC PATCH v3.1 14/27] mmc: sdhci-uhs2: skip
 signal_voltage_switch()

On Thu, Nov 26, 2020 at 10:16:44AM +0200, Adrian Hunter wrote:
> On 6/11/20 4:27 am, AKASHI Takahiro wrote:
> > For UHS2, the signal voltage is supplied by vdd2 which is already 1.8v,
> > so no voltage switch required.
> > 
> > Signed-off-by: Ben Chuang <ben.chuang@...esyslogic.com.tw>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > ---
> >  drivers/mmc/host/sdhci-uhs2.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> > 
> > diff --git a/drivers/mmc/host/sdhci-uhs2.c b/drivers/mmc/host/sdhci-uhs2.c
> > index 2bf78cc4e9ed..1eca89359351 100644
> > --- a/drivers/mmc/host/sdhci-uhs2.c
> > +++ b/drivers/mmc/host/sdhci-uhs2.c
> > @@ -178,6 +178,29 @@ void sdhci_uhs2_set_power(struct sdhci_host *host, unsigned char mode,
> >  }
> >  EXPORT_SYMBOL_GPL(sdhci_uhs2_set_power);
> >  
> > +/*****************************************************************************\
> > + *                                                                           *
> > + * MMC callbacks                                                             *
> > + *                                                                           *
> > +\*****************************************************************************/
> > +
> > +static int sdhci_uhs2_start_signal_voltage_switch(struct mmc_host *mmc,
> > +						  struct mmc_ios *ios)
> > +{
> > +	struct sdhci_host *host = mmc_priv(mmc);
> > +
> > +	/*
> > +	 * For UHS2, the signal voltage is supplied by vdd2 which is
> > +	 * already 1.8v so no voltage switch required.
> > +	 */
> > +        if (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > +             host->version >= SDHCI_SPEC_400 &&
> > +             host->mmc->flags & MMC_UHS2_SUPPORT)
> 
> Could this be the same helper function suggested elsewhere i.e.
> 
> 	if (!sdhci_uhs2_mode(host))


ditto. I'd defer the change until some time later.

-Takahiro Akashi

> 
> > +                return 0;
> > +
> > +	return sdhci_start_signal_voltage_switch(mmc, ios);
> > +}
> > +
> >  /*****************************************************************************\
> >   *                                                                           *
> >   * Driver init/exit                                                          *
> > @@ -186,6 +209,9 @@ EXPORT_SYMBOL_GPL(sdhci_uhs2_set_power);
> >  
> >  static int sdhci_uhs2_host_ops_init(struct sdhci_host *host)
> >  {
> > +	host->mmc_host_ops.start_signal_voltage_switch =
> > +		sdhci_uhs2_start_signal_voltage_switch;
> > +
> >  	return 0;
> >  }
> >  
> > 
>