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Subject: Re: [PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as
 NODATA
To:     Jason Yan <yanaijie@huawei.com>, Jolly Shah <jollys@google.com>,
        <jejb@linux.ibm.com>, <martin.petersen@oracle.com>,
        <a.darwish@linutronix.de>, <luojiaxing@huawei.com>,
        <dan.carpenter@oracle.com>, <b.zolnierkie@samsung.com>
CC:     <linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20210318225632.2481291-1-jollys@google.com>
 <5e7ea537-86ab-f654-1df4-765364116e18@huawei.com>
From:   John Garry <john.garry@huawei.com>
Message-ID: <993f97da-01f0-262b-3fbe-66fa1769698a@huawei.com>
Date:   Sat, 20 Mar 2021 12:14:52 +0000
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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@google.com>

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

@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;
>>
> .