linux-kernel - Re: [PATCH v4 2/6] tpm: tpm_tis_spi: Introduce a flow control callback

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Message-ID: <5d5ad721.1c69fb81.6a514.e649@mx.google.com>
Date:   Mon, 19 Aug 2019 10:06:40 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Peter Huewe <peterhuewe@....de>, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        Andrey Pronin <apronin@...omium.org>,
        Duncan Laurie <dlaurie@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <groeck@...omium.org>,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH v4 2/6] tpm: tpm_tis_spi: Introduce a flow control callback

Quoting Jarkko Sakkinen (2019-08-19 09:32:40)
> On Mon, Aug 12, 2019 at 03:36:18PM -0700, Stephen Boyd wrote:
> > Cr50 firmware has a different flow control protocol than the one used by
> > this TPM PTP SPI driver. Introduce a flow control callback so we can
> > override the standard sequence with the custom one that Cr50 uses.
> > 
> > Cc: Andrey Pronin <apronin@...omium.org>
> > Cc: Duncan Laurie <dlaurie@...omium.org>
> > Cc: Jason Gunthorpe <jgg@...pe.ca>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Guenter Roeck <groeck@...omium.org>
> > Cc: Alexander Steffen <Alexander.Steffen@...ineon.com>
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> > ---
> >  drivers/char/tpm/tpm_tis_spi.c | 55 +++++++++++++++++++++-------------
> >  1 file changed, 34 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
> > index 19513e622053..819602e85b34 100644
> > --- a/drivers/char/tpm/tpm_tis_spi.c
> > +++ b/drivers/char/tpm/tpm_tis_spi.c
> > @@ -42,6 +42,8 @@
> >  struct tpm_tis_spi_phy {
> >       struct tpm_tis_data priv;
> >       struct spi_device *spi_device;
> > +     int (*flow_control)(struct tpm_tis_spi_phy *phy,
> > +                         struct spi_transfer *xfer);
> >       u8 *iobuf;
> >  };
> >  
> > @@ -50,12 +52,39 @@ static inline struct tpm_tis_spi_phy *to_tpm_tis_spi_phy(struct tpm_tis_data *da
> >       return container_of(data, struct tpm_tis_spi_phy, priv);
> >  }
> >  
> > +static int tpm_tis_spi_flow_control(struct tpm_tis_spi_phy *phy,
> > +                                 struct spi_transfer *spi_xfer)
> > +{
> > +     struct spi_message m;
> > +     int ret, i;
> > +
> > +     if ((phy->iobuf[3] & 0x01) == 0) {
> > +             // handle SPI wait states
> > +             phy->iobuf[0] = 0;
> > +
> > +             for (i = 0; i < TPM_RETRY; i++) {
> > +                     spi_xfer->len = 1;
> > +                     spi_message_init(&m);
> > +                     spi_message_add_tail(spi_xfer, &m);
> > +                     ret = spi_sync_locked(phy->spi_device, &m);
> > +                     if (ret < 0)
> > +                             return ret;
> > +                     if (phy->iobuf[0] & 0x01)
> > +                             break;
> > +             }
> > +
> > +             if (i == TPM_RETRY)
> > +                     return -ETIMEDOUT;
> > +     }
> > +
> > +     return 0;
> > +}
> 
> AFAIK the flow control is not part of the SPI standard itself but is
> proprietary for each slave device. Thus, the flow control should be
> documented to the source code. I do not want flow control mechanisms to
> be multiplied before this is done.

Can you clarify this please? I don't understand what "the flow control
should be documented to the source code" means.

> 
> The magic number 0x01 would be also good to get rid off.
> 

Ok. What name should the #define be? I can make that another patch.