Hi John,
Thanks for the review.
On Wed, Mar 17, 2021 at 4:44 AM John Garry <john.garry@xxxxxxxxxx> wrote:
>
> On 16/03/2021 19:39, Jolly Shah wrote:
> > When the cache_type for the scsi device is changed, the scsi layer
> > issues a MODE_SELECT command. The caching mode details are communicated
> > via a request buffer associated with the scsi command with data
> > direction set as DMA_TO_DEVICE (scsi_mode_select). When this command
> > reaches the libata layer, as a part of generic initial setup, libata
> > layer sets up the scatterlist for the command using the scsi command
> > (ata_scsi_qc_new). This command is then translated by the libata layer
> > into ATA_CMD_SET_FEATURES (ata_scsi_mode_select_xlat). The libata layer
> > treats this as a non data command (ata_mselect_caching), since it only
> > needs an ata taskfile to pass the caching on/off information to the
> > device. It does not need the scatterlist that has been setup, so it does
> > not perform dma_map_sg on the scatterlist (ata_qc_issue).
>
> So if we don't perform the dma_map_sg() on the sgl at this point, then
> it seems to me that we should not perform for_each_sg() on it either,
> right? That is still what happens in sas_ata_qc_issue() in this case.
>
Yes that's right. To avoid that, I can add elseif block for
ATA_PROT_NODATA before for_each_sg() is performed. Currently there's
existing code block for ATA_PROT_NODATA after for_each_sg() is
performed,
reused that to reset num_scatter. Please suggest.
> > Unfortunately,
> > when this command reaches the libsas layer(sas_ata_qc_issue), libsas
> > layer sees it as a non data command with a scatterlist. It cannot
> > extract the correct dma length, since the scatterlist has not been
> > mapped with dma_map_sg for a DMA operation. When this partially
> > constructed SAS task reaches pm80xx LLDD, it results in below warning.
> >
> > "pm80xx_chip_sata_req 6058: The sg list address
> > start_addr=0x0000000000000000 data_len=0x0end_addr_high=0xffffffff
> > end_addr_low=0xffffffff has crossed 4G boundary"
> >
> > This patch assigns appropriate value to num_sectors for ata non data
> > commands.
> >
> > Signed-off-by: Jolly Shah <jollys@xxxxxxxxxx>
> > ---
> > drivers/scsi/libsas/sas_ata.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
> > index 024e5a550759..94ec08cebbaa 100644
> > --- a/drivers/scsi/libsas/sas_ata.c
> > +++ b/drivers/scsi/libsas/sas_ata.c
> > @@ -209,10 +209,12 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
> > task->num_scatter = si;
> > }
> >
> > - if (qc->tf.protocol == ATA_PROT_NODATA)
> > + if (qc->tf.protocol == ATA_PROT_NODATA) {
> > task->data_dir = DMA_NONE;
> > - else
> > + task->num_scatter = 0;
>
> task->num_scatter has already been set in this function. Best not set it
> twice.
>
Sure. Please suggest if I should update patch to above suggested
approach. That will avoid setting num_scatter twice.
Thanks,
Jolly Shah
> Thanks,
> John
>
> > + } else {
> > task->data_dir = qc->dma_dir;
> > + }
> > task->scatter = qc->sg;
> > task->ata_task.retry_count = 1;
> > task->task_state_flags = SAS_TASK_STATE_PENDING;
> >
>
