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SubjectRe: [PATCH 1/3] fsi: occ: Force sequence numbering per OCC
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On Wed, 2021-07-21 at 02:37 +0000, Joel Stanley wrote:
> 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?

It definitely could, I had the idea to do the checksumming outside the
mutex in case it took a long time? Probably not worth it though.

>
> 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.

Well, it doesn't really matter in fsi_occ_submit vs occ_putsram, as the
latter is only called in the former. occ_write wouldn't be used by the
hwmon interface, which is why we're moving some of that to
fsi_occ_submit, to have more in common. Agree it could probably be
organized better but I don't immediately have a good idea how to do
that.

Thanks for the review!
Eddie

>
>
>
> > 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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