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SubjectRe: [PATCH 1/3] fsi: occ: Force sequence numbering per OCC
On Fri, 16 Jul 2021 at 15:19, Eddie James <eajames@linux.ibm.com> wrote:
>
> Set and increment the sequence number during the submit operation.
> This prevents sequence number conflicts between different users of
> the interface. A sequence number conflict may result in a user
> getting an OCC response meant for a different command. Since the
> sequence number is now modified, the checksum must be calculated and
> set before submitting the command.
>
> Signed-off-by: Eddie James <eajames@linux.ibm.com>

Reviewed-by: Joel Stanley <joel@jms.id.au>

> @@ -479,11 +483,26 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
> return -EINVAL;
> }
>
> + /* Checksum the request, ignoring first byte (sequence number). */
> + for (i = 1; i < req_len - 2; ++i)
> + checksum += byte_request[i];
> +

This could go below, after you've got the sequence number, so the
checksumming all happens in the same spot?

The driver has become a bit of a maze, I can't tell how you're
deciding what goes in fsi_occ_submit vs occ_write vs occ_putsram. If
oyu have some ideas on how to simplify it then I would welcome those
changes.



> mutex_lock(&occ->occ_lock);
>
> - /* Extract the seq_no from the command (first byte) */
> - seq_no = *(const u8 *)request;
> - rc = occ_putsram(occ, request, req_len);
> + /*
> + * Get a sequence number and update the counter. Avoid a sequence
> + * number of 0 which would pass the response check below even if the
> + * OCC response is uninitialized. Any sequence number the user is
> + * trying to send is overwritten since this function is the only common
> + * interface to the OCC and therefore the only place we can guarantee
> + * unique sequence numbers.
> + */
> + seq_no = occ->sequence_number++;
> + if (!occ->sequence_number)
> + occ->sequence_number = 1;
> + checksum += seq_no;
> +
> + rc = occ_putsram(occ, request, req_len, seq_no, checksum);
> if (rc)
> goto done;

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