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

[luojiaxing]

On 2021/4/2 6:34, Jolly Shah wrote:
> Hi Luojiaxing,
>
>
> On Mon, Mar 22, 2021 at 1:41 AM luojiaxing <luojiaxing@xxxxxxxxxx> wrote:
> > On 2021/3/20 20:14, John Garry wrote:
> > > 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?
> >
> > Sure, let me take a look, and reply the test result here later
> Wanted to follow up on test results. Any updates?


Sorry for reply to you so late.


I use sdparm to change cache type of SATA disk, and it's ok with my test.

In addition, some other functional tests result have no problem too, So 
I think this patch is ok to me.


Tested-by: Luo Jiaxing <luojiaxing@xxxxxxxxxx>


Thanks

Jiaxing


> Thanks,
> Jolly
>
> > Thanks
> >
> > Jiaxing
> >
> >
> > > > > ---
> > > > > 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;
> > > > .
> > >
> > > .
> .