linux-kernel - Re: [PATCH] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

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Date:   Wed, 17 Mar 2021 10:11:57 -0700
From:   Jolly Shah <jollys@...gle.com>
To:     Jason Yan <yanaijie@...wei.com>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        john.garry@...wei.com, a.darwish@...utronix.de,
        luojiaxing@...wei.com, dan.carpenter@...cle.com,
        b.zolnierkie@...sung.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

Hi Jason,

Thanks for the review.


On Tue, Mar 16, 2021 at 6:50 PM Jason Yan <yanaijie@...wei.com> wrote:
>
>
> 在 2021/3/17 3:39, 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 assigns appropriate value to  num_sectors for ata non data
> > commands.
> >
> > Signed-off-by: Jolly Shah <jollys@...gle.com>
> > ---
> >   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;
> > +     } 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;
> >
>
> Thanks for the patch. Except the warning, any functional errors?
>

No functional errors observed.

Thanks,
Jolly Shah

> The code looks good to me,
>
> Reviewed-by: Jason Yan <yanaijie@...wei.com>