From eac9347d932b96c09f089ac0673ebe588983e59b Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Thu, 28 May 2020 15:19:30 -0700 Subject: [PATCH] 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 Reviewed-by: Paul Menzel Reviewed-by: Jarkko Sakkinen Signed-off-by: Jarkko Sakkinen --- 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; - 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; -- 2.11.0