Re: [PATCH v2 2/2] ata: libata-sata: Fix device queue depth control

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 9/26/22 20:31, John Garry wrote:
> On 26/09/2022 00:08, Damien Le Moal wrote:
>> The function __ata_change_queue_depth() uses the helper
>> ata_scsi_find_dev() to get the ata_device structure of a scsi device and
>> set that device maximum queue depth. However, when the ata device is
>> managed by libsas,
> 
> Yeah, this current code is utterly broken. Just a nit is that it would 
> be good to mention that the sdev id is assigned by scsi_transport_sas 
> (and not libata) for when using libsas.
> 
> In my series "Allocate SCSI device earlier for ata port probe" I 
> mentioned this problem of different id assignment scheme. It would be 
> nice to try to commonize this.
> 
>> ata_scsi_find_dev() returns NULL, turning
>> __ata_change_queue_depth() into a nop, which prevents the user from
>> setting the maximum queue depth of ATA devices used with libsas based
>> HBAs.
>>
>> Fix this by renaming __ata_change_queue_depth() to
>> ata_change_queue_depth() and adding a pointer to the ata_device
>> structure of the target device as argument. This pointer is provided by
>> ata_scsi_change_queue_depth() using ata_scsi_find_dev() in the case of
>> a libata managed device and by sas_change_queue_depth() using
>> sas_to_ata_dev() in the case of a libsas managed ata device.
> 
> This seems ok. But could you alternatively use ata_for_each_dev() and 
> match by ata_device.sdev pointer? That pointer is set quite late in the 
> probe, though, so maybe it would not work.

Not sure I understand why we should search for the ata device again using
ata_for_each_dev() when sas_to_ata_dev() gives us directly what we need
for the libsas controlled device... Can you clarify ?

> 
> As an aside, one other thing I noticed is that ata_device.private_data 
> is unused. Maybe we should delete it - apparently it was added just for 
> symmetry of libata structures.
> 
> Thanks,
> John
> 
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
>> ---
>>   drivers/ata/libata-sata.c           | 24 ++++++++++++------------
>>   drivers/scsi/libsas/sas_scsi_host.c |  3 ++-
>>   include/linux/libata.h              |  4 ++--
>>   3 files changed, 16 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
>> index 7a5fe41aa5ae..13b9d0fdd42c 100644
>> --- a/drivers/ata/libata-sata.c
>> +++ b/drivers/ata/libata-sata.c
>> @@ -1018,26 +1018,25 @@ DEVICE_ATTR(sw_activity, S_IWUSR | S_IRUGO, ata_scsi_activity_show,
>>   EXPORT_SYMBOL_GPL(dev_attr_sw_activity);
>>   
>>   /**
>> - *	__ata_change_queue_depth - helper for ata_scsi_change_queue_depth
>> - *	@ap: ATA port to which the device change the queue depth
>> + *	ata_change_queue_depth - Set a device maximum queue depth
>> + *	@ap: ATA port of the target device
>> + *	@dev: target ATA device
>>    *	@sdev: SCSI device to configure queue depth for
>>    *	@queue_depth: new queue depth
>>    *
>> - *	libsas and libata have different approaches for associating a sdev to
>> - *	its ata_port.
>> + *	Helper to set a device maximum queue depth, usable with both libsas
>> + *	and libata.
>>    *
>>    */
>> -int __ata_change_queue_depth(struct ata_port *ap, struct scsi_device *sdev,
>> -			     int queue_depth)
>> +int ata_change_queue_depth(struct ata_port *ap, struct ata_device *dev,
>> +			   struct scsi_device *sdev, int queue_depth)
>>   {
>> -	struct ata_device *dev;
>>   	unsigned long flags;
>>   
>> -	if (queue_depth < 1 || queue_depth == sdev->queue_depth)
>> +	if (!dev || !ata_dev_enabled(dev))
>>   		return sdev->queue_depth;
>>   
>> -	dev = ata_scsi_find_dev(ap, sdev);
>> -	if (!dev || !ata_dev_enabled(dev))
>> +	if (queue_depth < 1 || queue_depth == sdev->queue_depth)
>>   		return sdev->queue_depth;
>>   
>>   	/* NCQ enabled? */
>> @@ -1059,7 +1058,7 @@ int __ata_change_queue_depth(struct ata_port *ap, struct scsi_device *sdev,
>>   
>>   	return scsi_change_queue_depth(sdev, queue_depth);
>>   }
>> -EXPORT_SYMBOL_GPL(__ata_change_queue_depth);
>> +EXPORT_SYMBOL_GPL(ata_change_queue_depth);
>>   
>>   /**
>>    *	ata_scsi_change_queue_depth - SCSI callback for queue depth config
>> @@ -1080,7 +1079,8 @@ int ata_scsi_change_queue_depth(struct scsi_device *sdev, int queue_depth)
>>   {
>>   	struct ata_port *ap = ata_shost_to_port(sdev->host);
>>   
>> -	return __ata_change_queue_depth(ap, sdev, queue_depth);
>> +	return ata_change_queue_depth(ap, ata_scsi_find_dev(ap, sdev),
>> +				      sdev, queue_depth);
>>   }
>>   EXPORT_SYMBOL_GPL(ata_scsi_change_queue_depth);
>>   
>> diff --git a/drivers/scsi/libsas/sas_scsi_host.c b/drivers/scsi/libsas/sas_scsi_host.c
>> index 9c82e5dc4fcc..a36fa1c128a8 100644
>> --- a/drivers/scsi/libsas/sas_scsi_host.c
>> +++ b/drivers/scsi/libsas/sas_scsi_host.c
>> @@ -872,7 +872,8 @@ int sas_change_queue_depth(struct scsi_device *sdev, int depth)
>>   	struct domain_device *dev = sdev_to_domain_dev(sdev);
>>   
>>   	if (dev_is_sata(dev))
>> -		return __ata_change_queue_depth(dev->sata_dev.ap, sdev, depth);
>> +		return ata_change_queue_depth(dev->sata_dev.ap,
>> +					      sas_to_ata_dev(dev), sdev, depth);
>>   
>>   	if (!sdev->tagged_supported)
>>   		depth = 1;
>> diff --git a/include/linux/libata.h b/include/linux/libata.h
>> index 698032e5ef2d..20765d1c5f80 100644
>> --- a/include/linux/libata.h
>> +++ b/include/linux/libata.h
>> @@ -1136,8 +1136,8 @@ extern int ata_scsi_slave_config(struct scsi_device *sdev);
>>   extern void ata_scsi_slave_destroy(struct scsi_device *sdev);
>>   extern int ata_scsi_change_queue_depth(struct scsi_device *sdev,
>>   				       int queue_depth);
>> -extern int __ata_change_queue_depth(struct ata_port *ap, struct scsi_device *sdev,
>> -				    int queue_depth);
>> +extern int ata_change_queue_depth(struct ata_port *ap, struct ata_device *dev,
>> +				  struct scsi_device *sdev, int queue_depth);
>>   extern struct ata_device *ata_dev_pair(struct ata_device *adev);
>>   extern int ata_do_set_mode(struct ata_link *link, struct ata_device **r_failed_dev);
>>   extern void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap);
> 

-- 
Damien Le Moal
Western Digital Research