Messages in this thread Patch in this message | | | Subject | Re: [PATCH] scsi: libsas: Reset num_scatter if libata mark qc as NODATA | From | John Garry <> | Date | Thu, 18 Mar 2021 16:17:11 +0000 |
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On 18/03/2021 00:24, Jolly Shah wrote: > Hi John, > > Thanks for the review. > > > On Wed, Mar 17, 2021 at 4:44 AM John Garry <john.garry@huawei.com> 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. >>
Hi Jolly Shah,
> > 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. >
How about just combine the 2x if-else statements into 1x if-elif-else statement, like:
if (ata_is_atapi(qc->tf.protocol)) { 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; } 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; task->data_dir = qc->dma_dir; }
>>> 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@google.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; >> >> 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, John
BTW, could we add a fixes tag?
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