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

[PATCH] 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 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;
+	} 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] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

[Jason Yan]

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@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;
> +	} 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?

The code looks good to me,

Reviewed-by: Jason Yan <yanaijie@huawei.com>

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

[John Garry]

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.

> 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.

Thanks,
John

> +	} 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] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

[Jolly Shah]

Hi Jason,

Thanks for the review.


On Tue, Mar 16, 2021 at 6:50 PM Jason Yan <yanaijie@huawei.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@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;
> > +     } 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@huawei.com>

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

[Jolly Shah]

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.
>

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.

> > 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,
Jolly Shah

> Thanks,
> John
>
> > +     } 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] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

[John Garry]

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?

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

[Jolly Shah]

Hi John,


On Thu, Mar 18, 2021 at 9:19 AM John Garry <john.garry@huawei.com> wrote:
>
> 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;
> }
>
Updated in v2.

> >>> 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?

Added in v2.

Thanks,
Jolly