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

[John Garry <john.garry@xxxxxxxxxx>]

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.

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@xxxxxxxxxxxxxxxxxx>
> ---
>   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);