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authorDouglas Anderson <dianders@chromium.org>2020-05-28 15:19:30 -0700
committerJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>2020-07-02 17:48:59 +0300
commiteac9347d932b96c09f089ac0673ebe588983e59b (patch)
tree118ee9b2a571c853a87d497bae52336534831076 /drivers/char
parent7862840219058436b80029a0263fd1ef065fb1b3 (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')
-rw-r--r--drivers/char/tpm/tpm_tis_spi_main.c9
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;