Re: [PATCH v3 1/7] ata: libata-sata: Factor out NCQ Priority configuration helpers

[John Garry <john.g.garry@oracle.com>]

On 02/03/2024 20:16, Igor Pylypiv wrote:
> Export libata NCQ Priority configuration helpers to be reused
> for libsas managed SATA devices.
> 
> Signed-off-by: Igor Pylypiv <ipylypiv@google.com>

This looks ok. Some small code comments below, though.

> ---
>   drivers/ata/libata-sata.c | 139 +++++++++++++++++++++++++++-----------
>   include/linux/libata.h    |   4 ++
>   2 files changed, 103 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
> index 0fb1934875f2..a8d5e36d5211 100644
> --- a/drivers/ata/libata-sata.c
> +++ b/drivers/ata/libata-sata.c
> @@ -848,29 +848,73 @@ DEVICE_ATTR(link_power_management_policy, S_IRUGO | S_IWUSR,
>   	    ata_scsi_lpm_show, ata_scsi_lpm_store);
>   EXPORT_SYMBOL_GPL(dev_attr_link_power_management_policy);
>   
> +/**
> + *	ata_ncq_prio_supported - Check if device supports NCQ Priority
> + *	@ap: ATA port of the target device
> + *	@sdev: SCSI device
> + *
> + *	Helper to check if device supports NCQ Priority feature,
> + *	usable with both libsas and libata.
> + */
> +int ata_ncq_prio_supported(struct ata_port *ap, struct scsi_device *sdev)
> +{
> +	struct ata_device *dev;
> +	unsigned long flags;
> +	int rc;
> +
> +	spin_lock_irqsave(ap->lock, flags);
> +	dev = ata_scsi_find_dev(ap, sdev);
> +	if (!dev)
> +		rc = -ENODEV;
> +	else
> +		rc = !!(dev->flags & ATA_DFLAG_NCQ_PRIO);
> +	spin_unlock_irqrestore(ap->lock, flags);
> +	return rc;
> +}

I'm not the biggest fan of functions which effectively return both a 
boolean and an error code.

I like this patten more:

int ata_ncq_prio_supported(struct ata_port *ap, struct scsi_device 
*sdev, bool *supported)
{
	...
	if (rc)
		return rc;
	*supported = true/false.
	return 0;
}

No big deal, though.

> +EXPORT_SYMBOL_GPL(ata_ncq_prio_supported);
> +
>   static ssize_t ata_ncq_prio_supported_show(struct device *device,
>   					   struct device_attribute *attr,
>   					   char *buf)
>   {
>   	struct scsi_device *sdev = to_scsi_device(device);
>   	struct ata_port *ap = ata_shost_to_port(sdev->host);
> +	int rc;
> +
> +	rc = ata_ncq_prio_supported(ap, sdev);
> +	if (rc < 0)
> +		return rc;
> +
> +	return sysfs_emit(buf, "%d\n", rc);
> +}
> +
> +DEVICE_ATTR(ncq_prio_supported, S_IRUGO, ata_ncq_prio_supported_show, NULL);
> +EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_supported);
> +
> +/**
> + *	ata_ncq_prio_enabled - Check if NCQ Priority is enabled
> + *	@ap: ATA port of the target device
> + *	@sdev: SCSI device
> + *
> + *	Helper to check if NCQ Priority feature is enabled,
> + *	usable with both libsas and libata.

It's usable by anything which uses libata, really. For the moment that 
is libsas and libata.

> + */
> +int ata_ncq_prio_enabled(struct ata_port *ap, struct scsi_device *sdev)
> +{
>   	struct ata_device *dev;
> -	bool ncq_prio_supported;
> -	int rc = 0;
> +	unsigned long flags;
> +	int rc;
>   
> -	spin_lock_irq(ap->lock);
> +	spin_lock_irqsave(ap->lock, flags);
>   	dev = ata_scsi_find_dev(ap, sdev);
>   	if (!dev)
>   		rc = -ENODEV;
>   	else
> -		ncq_prio_supported = dev->flags & ATA_DFLAG_NCQ_PRIO;
> -	spin_unlock_irq(ap->lock);
> -
> -	return rc ? rc : sysfs_emit(buf, "%u\n", ncq_prio_supported);
> +		rc = !!(dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED);
> +	spin_unlock_irqrestore(ap->lock, flags);
> +	return rc;
>   }
> -
> -DEVICE_ATTR(ncq_prio_supported, S_IRUGO, ata_ncq_prio_supported_show, NULL);
> -EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_supported);
> +EXPORT_SYMBOL_GPL(ata_ncq_prio_enabled);
>   
>   static ssize_t ata_ncq_prio_enable_show(struct device *device,
>   					struct device_attribute *attr,
> @@ -878,50 +922,45 @@ static ssize_t ata_ncq_prio_enable_show(struct device *device,
>   {
>   	struct scsi_device *sdev = to_scsi_device(device);
>   	struct ata_port *ap = ata_shost_to_port(sdev->host);
> -	struct ata_device *dev;
> -	bool ncq_prio_enable;
> -	int rc = 0;
> +	int rc;
>   
> -	spin_lock_irq(ap->lock);
> -	dev = ata_scsi_find_dev(ap, sdev);
> -	if (!dev)
> -		rc = -ENODEV;
> -	else
> -		ncq_prio_enable = dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED;
> -	spin_unlock_irq(ap->lock);
> +	rc = ata_ncq_prio_enabled(ap, sdev);
> +	if (rc < 0)
> +		return rc;
>   
> -	return rc ? rc : sysfs_emit(buf, "%u\n", ncq_prio_enable);
> +	return sysfs_emit(buf, "%d\n", rc);
>   }
>   
> -static ssize_t ata_ncq_prio_enable_store(struct device *device,
> -					 struct device_attribute *attr,
> -					 const char *buf, size_t len)
> +/**
> + *	ata_ncq_prio_enable - Enable/disable NCQ Priority
> + *	@ap: ATA port of the target device
> + *	@sdev: SCSI device
> + *	@enable: true - enable NCQ Priority, false - disable NCQ Priority
> + *
> + *	Helper to enable/disable NCQ Priority feature, usable with both
> + *	libsas and libata.
> + */
> +int ata_ncq_prio_enable(struct ata_port *ap, struct scsi_device *sdev,
> +			bool enable)
>   {
> -	struct scsi_device *sdev = to_scsi_device(device);
> -	struct ata_port *ap;
>   	struct ata_device *dev;
> -	long int input;
> +	unsigned long flags;
>   	int rc = 0;
>   
> -	rc = kstrtol(buf, 10, &input);
> -	if (rc)
> -		return rc;
> -	if ((input < 0) || (input > 1))
> -		return -EINVAL;
> +	spin_lock_irqsave(ap->lock, flags);
>   
> -	ap = ata_shost_to_port(sdev->host);
>   	dev = ata_scsi_find_dev(ap, sdev);
> -	if (unlikely(!dev))
> -		return  -ENODEV;
> -
> -	spin_lock_irq(ap->lock);
> +	if (unlikely(!dev)) {

no need for unlikely() - this is not fathpath

> +		rc = -ENODEV;
> +		goto unlock;
> +	}
>   
>   	if (!(dev->flags & ATA_DFLAG_NCQ_PRIO)) {
>   		rc = -EINVAL;
>   		goto unlock;