Hi Ming,
On Fri, 14 Jun 2019, Ming Lei wrote:
> Use the scatterlist iterators and remove direct indexing of the
> scatterlist array.
>
> This way allows us to pre-allocate one small scatterlist, which can be
> chained with one runtime allocated scatterlist if the pre-allocated one
> isn't enough for the whole request.
>
> Signed-off-by: Ming Lei <ming....@redhat.com>
> ---
> drivers/scsi/aha152x.c | 29 +++++++++++++++++++----------
> 1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/scsi/aha152x.c b/drivers/scsi/aha152x.c
> index 97872838b983..bc9d12aa7880 100644
> --- a/drivers/scsi/aha152x.c
> +++ b/drivers/scsi/aha152x.c
> @@ -2033,7 +2033,7 @@ static void datai_run(struct Scsi_Host *shpnt)
> CURRENT_SC->SCp.buffers_residual > 0) {
> /* advance to next buffer */
> CURRENT_SC->SCp.buffers_residual--;
> - CURRENT_SC->SCp.buffer++;
> + CURRENT_SC->SCp.buffer =
> sg_next(CURRENT_SC->SCp.buffer);
> CURRENT_SC->SCp.ptr =
> SG_ADDRESS(CURRENT_SC->SCp.buffer);
> CURRENT_SC->SCp.this_residual =
> CURRENT_SC->SCp.buffer->length;
> }
> @@ -2139,7 +2139,7 @@ static void datao_run(struct Scsi_Host *shpnt)
> if(CURRENT_SC->SCp.this_residual==0 &&
> CURRENT_SC->SCp.buffers_residual>0) {
> /* advance to next buffer */
> CURRENT_SC->SCp.buffers_residual--;
> - CURRENT_SC->SCp.buffer++;
> + CURRENT_SC->SCp.buffer =
> sg_next(CURRENT_SC->SCp.buffer);
> CURRENT_SC->SCp.ptr =
> SG_ADDRESS(CURRENT_SC->SCp.buffer);
> CURRENT_SC->SCp.this_residual =
> CURRENT_SC->SCp.buffer->length;
> }
> @@ -2160,20 +2160,29 @@ static void datao_end(struct Scsi_Host *shpnt)
> if(TESTLO(DMASTAT, DFIFOEMP)) {
> int data_count = (DATA_LEN - scsi_get_resid(CURRENT_SC)) -
> GETSTCNT();
data_count appears to be the number of bytes remaining in the FIFO. (I
have to infer that much from the surrounding code. I don't have
documentation for this controller.)
Some comments would be nice.
> + struct scatterlist *sg = scsi_sglist(CURRENT_SC);
> + int left, i = 0;
>
> CMD_INC_RESID(CURRENT_SC, data_count);
>
Apparently the aim is to increase the residual by the number of bytes that
will never leave the FIFO. Above we can see that increase performed by
scsi_set_resid() and now the same has to be done to the SCp struct.
> data_count -= CURRENT_SC->SCp.ptr -
> SG_ADDRESS(CURRENT_SC->SCp.buffer);
Here, data_count effectively has SCp.this_residual subtracted from it.
> - while(data_count>0) {
> - CURRENT_SC->SCp.buffer--;
> - CURRENT_SC->SCp.buffers_residual++;
> - data_count -= CURRENT_SC->SCp.buffer->length;
> - }
So far, so good.
> - CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer) -
> - data_count;
> - CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length +
> - data_count;
This is like saying ptr = buffer + residual, which is bogus. This must be
an old bug, but we never hit it because the FIFO is always empty when we
get a DISCONNECT message. Probably because every SG segment has a length
that is a multiple of 128 bytes. (Juergen?)
> +
> + left = CURRENT_SC->transfersize - data_count;
Are you sure about that? Perhaps you meant to write,
left = scsi_bufflen(CURRENT_SC) - scsi_get_resid(CURRENT_SC);
Is there a better name for this variable? Maybe 'sent' or 'bytes_sent'?
> + for (i = 0; left > 0 && !sg_is_last(sg); i++, sg = sg_next(sg))
> {
> + if (left < sg->length)
> + break;
> + left -= sg->length;
> + }
> +
> + if (data_count > 0) {
> + CURRENT_SC->SCp.buffers_residual += i;
Shouldn't that be,
CURRENT_SC->SCp.buffers_residual = i;
> + CURRENT_SC->SCp.buffer = sg;
> +
> + CURRENT_SC->SCp.ptr =
> SG_ADDRESS(CURRENT_SC->SCp.buffer) + left;
> + CURRENT_SC->SCp.this_residual =
> CURRENT_SC->SCp.buffer->length -
> + left;
> + }
> }
>
> SETPORT(SXFRCTL0, CH1|CLRCH1|CLRSTCNT);
>
BTW, datao_run() seems to guarantee that the FIFO will never contain more
than min(128, SCp.this_residual) so I suspect that this code can be
simplified. That's just BTW. I wouldn't attempt to optimize this branch as
it will only run when the FIFO is not empty, if ever. So I'd prefer
clarity. Besides, I don't have the hardware to test it on.
--
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