On Thu, May 28, 2020 at 03:19:30PM -0700, Douglas Anderson wrote: > During flow control we are just reading from the TPM, yet our spi_xfer > has the tx_buf and rx_buf both non-NULL which means we're requesting a > full duplex transfer. > > SPI is always somewhat of a full duplex protocol anyway and in theory > the other side shouldn't really be looking at what we're sending it > during flow control, but it's still a bit ugly to be sending some > "random" data when we shouldn't. > > The default tpm_tis_spi_flow_control() tries to address this by > setting 'phy->iobuf[0] = 0'. This partially avoids the problem of > sending "random" data, but since our tx_buf and rx_buf both point to > the same place I believe there is the potential of us sending the > TPM's previous byte back to it if we hit the retry loop. > > Another flow control implementation, cr50_spi_flow_control(), doesn't > address this at all. > > Let's clean this up and just make the tx_buf NULL before we call > flow_control(). Not only does this ensure that we're not sending any > "random" bytes but it also possibly could make the SPI controller > behave in a slightly more optimal way. > > NOTE: no actual observed problems are fixed by this patch--it's was > just made based on code inspection. > > Signed-off-by: Douglas Anderson <[email protected]> > --- > > drivers/char/tpm/tpm_tis_spi_main.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/drivers/char/tpm/tpm_tis_spi_main.c > b/drivers/char/tpm/tpm_tis_spi_main.c > index d96755935529..8d2c581a93c6 100644 > --- a/drivers/char/tpm/tpm_tis_spi_main.c > +++ b/drivers/char/tpm/tpm_tis_spi_main.c > @@ -53,8 +53,6 @@ static int tpm_tis_spi_flow_control(struct tpm_tis_spi_phy > *phy, > > if ((phy->iobuf[3] & 0x01) == 0) { > // handle SPI wait states > - phy->iobuf[0] = 0; > -
Why this should be removed? /Jarkko
