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

Jarkko Sakkinen
2019-08-19T16:32:50Z

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@chromium.org>
> Cc: Duncan Laurie <dlaurie@chromium.org>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Guenter Roeck <groeck@chromium.org>
> Cc: Alexander Steffen <Alexander.Steffen@infineon.com>
> Signed-off-by: Stephen Boyd <swboyd@chromium.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.

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

/Jarkko