linux-kernel - Re: [PATCH 09/10] mmc: tegra: Perform pad calibration after voltage switch

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Date:   Wed, 25 Jul 2018 13:43:00 +0300
From:   Aapo Vienamo <avienamo@...dia.com>
To:     Mikko Perttunen <cyndis@...si.fi>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/10] mmc: tegra: Perform pad calibration after voltage
 switch

On Wed, 25 Jul 2018 10:25:16 +0300
Mikko Perttunen <cyndis@...si.fi> wrote:

> On 24.07.2018 17:34, Aapo Vienamo wrote:
> > Run the automatic pad calibration after voltage switching if
> > tegra_host->pad_calib_required is set.
> > 
> > Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> > ---
> >   drivers/mmc/host/sdhci-tegra.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> > index 78781bd..529aa4e7 100644
> > --- a/drivers/mmc/host/sdhci-tegra.c
> > +++ b/drivers/mmc/host/sdhci-tegra.c
> > @@ -537,6 +537,8 @@ static int sdhci_tegra_start_signal_voltage_switch(struct mmc_host *mmc,
> >   						   struct mmc_ios *ios)
> >   {
> >   	struct sdhci_host *host = mmc_priv(mmc);
> > +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> > +	struct sdhci_tegra *tegra_host = sdhci_pltfm_priv(pltfm_host);
> >   	int ret = 0;
> >   
> >   	if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_330) {
> > @@ -551,6 +553,9 @@ static int sdhci_tegra_start_signal_voltage_switch(struct mmc_host *mmc,
> >   		ret = tegra_sdhci_set_padctrl(host, ios->signal_voltage);
> >   	}
> >   
> > +	if (tegra_host->pad_calib_required)
> > +		tegra_sdhci_pad_autocalib(host);  
> 
> What if the autocalibration fails? Should we return an error?

I would assume that aborting the signal voltage switch due to a
calibration timeout would not be necessary as the TRM specifies drive
strength values which are to be programmed in case a timeout occurs.

However, I don't know what are the exact implications of running the bus
with the timeout values instead of the calibrated ones. The TRM does not
comment on that. I guess tuning would fail and catch the error that way
in case the timeout default values aren't sufficient.

 -Aapo

> > +
> >   	return ret;
> >   }
> >   
> >