Am 17. Februar 2017 06:09:42 MEZ schrieb Christophe Ricard <christophe.ricard@xxxxxxxxx>: >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. Yes - it would be perfect to fix the issue in the upstream rpi spi master driver. However this only happens sporadically in some strange cases (i.e. 300-500khz, single byte transfer after having more bytes in the same #cs frame) (unrelated to the tpm) We are still looking into it, why /where it happens and how to reproduce it reliably and then file a bug/fix it. For now however the priority is to make the tpm_tis_spi driver work reliably also on the rpi, and this is what this workaround does. We can simply remove it once the rpi spi master is fixed. Peter > > >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; -- Sent from my mobile