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

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

[Jolly Shah]

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>
---
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;
 	} 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;
-- 
2.31.0.rc2.261.g7f71774620-goog

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

[Jason Yan]

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>
> ---
> 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?

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;
> 

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@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;
>>
> .

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

[luojiaxing]

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@google.com>
>
> Reviewed-by: John Garry <john.garry@huawei.com>
>
> @luojiaxing, can you please test this?


Sure, let me take a look, and reply the test result here later


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;
>>>
>> .
>
>
> .
>

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

[Jolly Shah]

Hi Luojiaxing,


On Mon, Mar 22, 2021 at 1:41 AM luojiaxing <luojiaxing@huawei.com> 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@google.com>
> >
> > Reviewed-by: John Garry <john.garry@huawei.com>
> >
> > @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?

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;
> >>>
> >> .
> >
> >
> > .
> >
>

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


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;
>>>>>
>>>> .
>>>
>>> .
>>>
> .
>

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

[Martin K. Petersen]

On Thu, 18 Mar 2021 15:56:32 -0700, 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). 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.
> 
> [...]

Applied to 5.12/scsi-fixes, thanks!

[1/1] scsi: libsas: Reset num_scatter if libata mark qc as NODATA
      https://git.kernel.org/mkp/scsi/c/176ddd89171d

-- 
Martin K. Petersen	Oracle Linux Engineering