Re: [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer

From: Christophe Ricard
Date: Fri Feb 17 2017 - 00:09:51 EST

Are you sure it is not better to introduce this delay directly in the rpi spi driver ?

Other than that i don't see any issue with it.

On 16/02/2017 08:09, Peter Huewe wrote:
Testing the implementation with a Raspberry Pi 2 showed that under some
circumstances its SPI master erroneously releases the CS line before the
transfer is complete, i.e. before the end of the last clock. In this case
the TPM ignores the transfer and misses for example the GO command. The
driver is unable to detect this communication problem and will wait for a
command response that is never going to arrive, timing out eventually.

As a workaround, the small delay ensures that the CS line is held long
enough, even with a faulty SPI master. Other SPI masters are not affected,
except for a negligible performance penalty.

Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Signed-off-by: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx>
Signed-off-by: Peter Huewe <peter.huewe@xxxxxxxxxxxx>
drivers/char/tpm/tpm_tis_spi.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index b50c5b072df3..685c51bf5d7e 100644
--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -110,6 +110,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,
spi_xfer.cs_change = 0;
spi_xfer.len = transfer_len;
+ spi_xfer.delay_usecs = 5;
if (direction) {
spi_xfer.tx_buf = NULL;