diff options
| author | Douglas Anderson <dianders@chromium.org> | 2020-05-28 15:19:30 -0700 |
|---|---|---|
| committer | Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> | 2020-07-02 17:48:59 +0300 |
| commit | eac9347d932b96c09f089ac0673ebe588983e59b (patch) | |
| tree | 118ee9b2a571c853a87d497bae52336534831076 /drivers/char/tpm | |
| parent | 7862840219058436b80029a0263fd1ef065fb1b3 (diff) | |
tpm_tis_spi: Don't send anything during flow control
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 <dianders@chromium.org>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Diffstat (limited to 'drivers/char/tpm')
| -rw-r--r-- | drivers/char/tpm/tpm_tis_spi_main.c | 9 |
1 files 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; - for (i = 0; i < TPM_RETRY; i++) { spi_xfer->len = 1; spi_message_init(&m); @@ -104,6 +102,8 @@ int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len, if (ret < 0) goto exit; + /* Flow control transfers are receive only */ + spi_xfer.tx_buf = NULL; ret = phy->flow_control(phy, &spi_xfer); if (ret < 0) goto exit; @@ -113,9 +113,8 @@ int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len, spi_xfer.delay.value = 5; spi_xfer.delay.unit = SPI_DELAY_UNIT_USECS; - if (in) { - spi_xfer.tx_buf = NULL; - } else if (out) { + if (out) { + spi_xfer.tx_buf = phy->iobuf; spi_xfer.rx_buf = NULL; memcpy(phy->iobuf, out, transfer_len); out += transfer_len; |