RE: [Patch V9 2/3] tpm_tis-spi: Add hardware wait polling

[Krishna Yarlagadda]

> -----Original Message-----
> From: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> Sent: 20 April 2023 08:42
> To: Krishna Yarlagadda <kyarlagadda@xxxxxxxxxx>
> Cc: robh+dt@xxxxxxxxxx; broonie@xxxxxxxxxx; peterhuewe@xxxxxx;
> jgg@xxxxxxxx; jarkko@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; linux-
> spi@xxxxxxxxxxxxxxx; linux-tegra@xxxxxxxxxxxxxxx; linux-
> integrity@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> thierry.reding@xxxxxxxxx; Jonathan Hunter <jonathanh@xxxxxxxxxx>;
> Sowjanya Komatineni <skomatineni@xxxxxxxxxx>; Laxman Dewangan
> <ldewangan@xxxxxxxxxx>
> Subject: Re: [Patch V9 2/3] tpm_tis-spi: Add hardware wait polling
> 
> External email: Use caution opening links or attachments
> 
> 
> On Wed, Apr 19, 2023 at 07:32:40PM -0700, Jerry Snitselaar wrote:
> > On Sun, Mar 26, 2023 at 12:04:08AM +0530, Krishna Yarlagadda wrote:
> > > TPM devices may insert wait state on last clock cycle of ADDR phase.
> > > For SPI controllers that support full-duplex transfers, this can be
> > > detected using software by reading the MISO line. For SPI controllers
> > > that only support half-duplex transfers, such as the Tegra QSPI, it is
> > > not possible to detect the wait signal from software. The QSPI
> > > controller in Tegra234 and Tegra241 implement hardware detection of
> the
> > > wait signal which can be enabled in the controller for TPM devices.
> > >
> > > The current TPM TIS driver only supports software detection of the wait
> > > signal. To support SPI controllers that use hardware to detect the wait
> > > signal, add the function tpm_tis_spi_hw_flow_transfer() and move the
> > > existing code for software based detection into a function called
> > > tpm_tis_spi_sw_flow_transfer(). SPI controllers that only support
> > > half-duplex transfers will always call tpm_tis_spi_hw_flow_transfer()
> > > because they cannot support software based detection. The bit
> > > SPI_TPM_HW_FLOW is set to indicate to the SPI controller that hardware
> > > detection is required and it is the responsibility of the SPI controller
> > > driver to determine if this is supported or not.
> > >
> > > For hardware flow control, CMD-ADDR-DATA messages are combined
> into a
> > > single message where as for software flow control exiting method of
> > > CMD-ADDR in a message and DATA in another is followed.
> > >
> > > Signed-off-by: Krishna Yarlagadda <kyarlagadda@xxxxxxxxxx>
> > > ---
> > >  drivers/char/tpm/tpm_tis_spi_main.c | 91
> ++++++++++++++++++++++++++++-
> > >  1 file changed, 89 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/char/tpm/tpm_tis_spi_main.c
> b/drivers/char/tpm/tpm_tis_spi_main.c
> > > index a0963a3e92bd..db9afd0b83da 100644
> > > --- a/drivers/char/tpm/tpm_tis_spi_main.c
> > > +++ b/drivers/char/tpm/tpm_tis_spi_main.c
> > > @@ -71,8 +71,74 @@ static int tpm_tis_spi_flow_control(struct
> tpm_tis_spi_phy *phy,
> > >     return 0;
> > >  }
> > >
> > > -int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
> > > -                    u8 *in, const u8 *out)
> > > +/*
> > > + * Half duplex controller with support for TPM wait state detection like
> > > + * Tegra QSPI need CMD, ADDR & DATA sent in single message to
> manage HW flow
> > > + * control. Each phase sent in different transfer for controller to idenity
> > > + * phase.
> > > + */
> > > +static int tpm_tis_spi_transfer_half(struct tpm_tis_data *data,    u32
> addr,
> > > +                                u16 len, u8 *in, const u8 *out)
> > > +{
> > > +   struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
> > > +   struct spi_transfer spi_xfer[3];
> > > +   struct spi_message m;
> > > +   u8 transfer_len;
> > > +   int ret;
> > > +
> > > +   while (len) {
> > > +           transfer_len = min_t(u16, len, MAX_SPI_FRAMESIZE);
> > > +
> > > +           spi_message_init(&m);
> > > +           phy->iobuf[0] = (in ? 0x80 : 0) | (transfer_len - 1);
> > > +           phy->iobuf[1] = 0xd4;
> > > +           phy->iobuf[2] = addr >> 8;
> > > +           phy->iobuf[3] = addr;
> >
> > I haven't looked at much TPM code in the past couple of years, but
> > perhaps some defines instead of magic numbers here? 0x80 is the rw bit,
> > and 0xd4 the transaction offset?
> >
> > > +
> > > +           memset(&spi_xfer, 0, sizeof(spi_xfer));
> > > +
> > > +           spi_xfer[0].tx_buf = phy->iobuf;
> > > +           spi_xfer[0].len = 1;
> > > +           spi_message_add_tail(&spi_xfer[0], &m);
> > > +
> > > +           spi_xfer[1].tx_buf = phy->iobuf + 1;
> > > +           spi_xfer[1].len = 3;
> > > +           spi_message_add_tail(&spi_xfer[1], &m);
> > > +
> > > +           if (out) {
> > > +                   spi_xfer[2].tx_buf = &phy->iobuf[4];
> > > +                   spi_xfer[2].rx_buf = NULL;
> > > +                   memcpy(&phy->iobuf[4], out, transfer_len);
> > > +                   out += transfer_len;
> > > +           }
> > > +
> > > +           if (in) {
> > > +                   spi_xfer[2].tx_buf = NULL;
> > > +                   spi_xfer[2].rx_buf = &phy->iobuf[4];
> > > +           }
> > > +
> > > +           spi_xfer[2].len = transfer_len;
> > > +           spi_message_add_tail(&spi_xfer[2], &m);
> > > +
> > > +           reinit_completion(&phy->ready);
> > > +
> > > +           ret = spi_sync_locked(phy->spi_device, &m);
> > > +           if (ret < 0)
> > > +                   return ret;
> > > +
> > > +           if (in) {
> > > +                   memcpy(in, &phy->iobuf[4], transfer_len);
> > > +                   in += transfer_len;
> > > +           }
> > > +
> > > +           len -= transfer_len;
> > > +   }
> > > +
> > > +   return ret;
> > > +}
> >
> > Does tpm_tis_spi_transfer_half not need to lock the bus?  The doc
> comments for spi_sync_locked
> > state:
> >
> >  This call should be used by drivers that require exclusive access to the
> >  SPI bus. It has to be preceded by a spi_bus_lock call. The SPI bus must
> >  be released by a spi_bus_unlock call when the exclusive access is over.
> >
> > If that isn't the case should it be using spi_sync instead of spi_sync_locked?
> >
> > Regards,
> > Jerry
> 
> b4 mbox -c to the rescue. I found the earlier discussion with Mark about
> the lock, so I guess the question is just should this call spi_sync
> instead of spi_sync_locked then?
> 
> The magic numbers is a minor nit, and can probably be cleaned up
> separately since the full duplex code was already doing the same
> thing. The only other nit is just the older tcg spec being referenced
> in patch 1.
> 
> Regards,
> Jerry
Magic number can be dealt in a different patch for both half and full
Transfer calls.
As we send single message for complete transaction, bus need not be
locked. I will replace the calls with spi_sync.
Will update referenced tcg spec as well to the latest.

Regards
KY
> 
> >
> > > +
> > > +static int tpm_tis_spi_transfer_full(struct tpm_tis_data *data, u32 addr,
> > > +                                u16 len, u8 *in, const u8 *out)
> > >  {
> > >     struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
> > >     int ret = 0;
> > > @@ -140,6 +206,24 @@ int tpm_tis_spi_transfer(struct tpm_tis_data
> *data, u32 addr, u16 len,
> > >     return ret;
> > >  }
> > >
> > > +int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
> > > +                    u8 *in, const u8 *out)
> > > +{
> > > +   struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
> > > +   struct spi_controller *ctlr = phy->spi_device->controller;
> > > +
> > > +   /*
> > > +    * TPM flow control over SPI requires full duplex support.
> > > +    * Send entire message to a half duplex controller to handle
> > > +    * wait polling in controller.
> > > +    * Set TPM HW flow control flag..
> > > +    */
> > > +   if (ctlr->flags & SPI_CONTROLLER_HALF_DUPLEX)
> > > +           return tpm_tis_spi_transfer_half(data, addr, len, in, out);
> > > +   else
> > > +           return tpm_tis_spi_transfer_full(data, addr, len, in, out);
> > > +}
> > > +
> > >  static int tpm_tis_spi_read_bytes(struct tpm_tis_data *data, u32 addr,
> > >                               u16 len, u8 *result, enum tpm_tis_io_mode io_mode)
> > >  {
> > > @@ -181,6 +265,9 @@ static int tpm_tis_spi_probe(struct spi_device
> *dev)
> > >
> > >     phy->flow_control = tpm_tis_spi_flow_control;
> > >
> > > +   if (dev->controller->flags & SPI_CONTROLLER_HALF_DUPLEX)
> > > +           dev->mode |= SPI_TPM_HW_FLOW;
> > > +
> > >     /* If the SPI device has an IRQ then use that */
> > >     if (dev->irq > 0)
> > >             irq = dev->irq;
> > > --
> > > 2.17.1
> > >
> >