linux-kernel - Re: [PATCH 2/3] scsi: ufs: Allow resetting the UFS device

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Date:   Tue, 4 Jun 2019 15:20:10 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        Andy Gross <agross@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH 2/3] scsi: ufs: Allow resetting the UFS device

On Tue 04 Jun 08:25 PDT 2019, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2019-06-04 00:20:00)
> > @@ -6104,6 +6105,25 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> >         return err;
> >  }
> >  
> > +/**
> > + ufshcd_device_reset() - toggle the (optional) device reset line
> > + * @hba: per-adapter instance
> > + *
> > + * Toggles the (optional) reset line to reset the attached device.
> > + */
> > +static void ufshcd_device_reset(struct ufs_hba *hba)
> > +{
> > +       /*
> > +        * The USB device shall detect reset pulses of 1us, sleep for 10us to
> 
> This isn't usb though.

No, it is not.

> Can we have a gpio reset driver and then
> implement this in the reset framework instead? Or did that not work out
> for some reason?
> 

The reset DT binding document clearly describes that resets are for
chip-internal resets, and this is a general purpose (output-only) pad on
the SoC that's connected to the reset pin on the UFS memory.

I actually see nothing preventing you to connect said reset pin to any
other GPIO.

Regards,
Bjorn

> > +        * be on the safe side.
> > +        */
> > +       gpiod_set_value_cansleep(hba->device_reset, 1);
> > +       usleep_range(10, 15);
> > +
> > +       gpiod_set_value_cansleep(hba->device_reset, 0);
> > +       usleep_range(10, 15);
> > +}
> > +
> >  /**
> >   * ufshcd_host_reset_and_restore - reset and restore host controller
> >   * @hba: per-adapter instance