On Fri, Dec 08, 2017 at 07:46:53PM +0100, Alexander Steffen wrote: > tpm_tis_send_data splits all commands sent to the TPM into at least two > transfers, even if the commands are small enough to fit into a single > transfer. The intention seems to be to make extra sure that the TPM has > received all data correctly by observing the Expect flag flipping from 1 to > 0 when writing the last byte. > > Unfortunately, this does not work as intended, because the Expect flag will > change not when the last byte is written to the FIFO, but when the TPM > processes the last byte from the FIFO. With a large FIFO and long commands > it might well be that there are still many bytes left in the FIFO when the > Expect flag is checked. Obviously, the flag will be 1 then, even if the > FIFO contains more bytes than expected. Since there is no indication > whether the FIFO is already empty or not, there is no way to implement this > check reliably. > > But then again, this check is not necessary at all. The driver already > ensures that not more data is sent to the TPM than is announced in the > header. In addition, the TPM is required to throw away all extraneous bytes > anyway. So if the Expect flag is 0 after all bytes have been sent to the > TPM, the TPM has received the command correctly and is ready to execute it. > > Therefore, remove this intermediary check and send all data in a single > operation. This simplifies the code and improves the performance, > especially for short commands. > > Signed-off-by: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx> LGTM Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> /Jarkko
