Re: [PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

[John Garry]

On 19/03/2021 01:43, Jason Yan wrote:
> 在 2021/3/19 6:56, Jolly Shah 写道:
> > 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). 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 updates code to handle ata non data commands separately so
> > num_scatter and total_xfer_len remain 0.
> >
> > Fixes: 53de092f47ff ("scsi: libsas: Set data_dir as DMA_NONE if libata 
> > marks qc as NODATA")
> > Signed-off-by: Jolly Shah <jollys@xxxxxxxxxx>

Reviewed-by: John Garry <john.garry@xxxxxxxxxx>

@luojiaxing, can you please test this?

> > ---
> > v2:
> > - reorganized code to avoid setting num_scatter twice
> >
> >   drivers/scsi/libsas/sas_ata.c | 9 ++++-----
> >   1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/scsi/libsas/sas_ata.c 
> > b/drivers/scsi/libsas/sas_ata.c
> > index 024e5a550759..8b9a39077dba 100644
> > --- a/drivers/scsi/libsas/sas_ata.c
> > +++ b/drivers/scsi/libsas/sas_ata.c
> > @@ -201,18 +201,17 @@ static unsigned int sas_ata_qc_issue(struct 
> > ata_queued_cmd *qc)
> >           memcpy(task->ata_task.atapi_packet, qc->cdb, qc->dev->cdb_len);
> >           task->total_xfer_len = qc->nbytes;
> >           task->num_scatter = qc->n_elem;
> > +        task->data_dir = qc->dma_dir;
> > +    } else if (qc->tf.protocol == ATA_PROT_NODATA) {
> > +        task->data_dir = DMA_NONE;
>
> Hi Jolly & John,
>
> We only set DMA_NONE for ATA_PROT_NODATA, I'm curious about why 
> ATA_PROT_NCQ_NODATA and ATAPI_PROT_NODATA do not need to set DMA_NONE?

So we can see something like atapi_eh_tur() -> ata_exec_internal(), 
which is a ATAPI NONDATA and has DMA_NONE, so should be ok.

Other cases, like those using the xlate function on the qc for 
ATA_PROT_NCQ_NODATA, could be checked further.

For now, we're just trying to fix the fix.

> Thanks,
> Jason
>
>
> >       } else {
> >           for_each_sg(qc->sg, sg, qc->n_elem, si)
> >               xfer += sg_dma_len(sg);
> >           task->total_xfer_len = xfer;
> >           task->num_scatter = si;
> > -    }
> > -
> > -    if (qc->tf.protocol == ATA_PROT_NODATA)
> > -        task->data_dir = DMA_NONE;
> > -    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;
> .