Re: [PATCH v3 8/9] libahci: Introduce ncq_prio_supported sysfs sttribute

[Hannes Reinecke <hare@suse.de>]

On 8/6/21 1:11 PM, Damien Le Moal wrote:
> Currently, the only way a user can determine if a SATA device supports
> NCQ priority is to try to enable the use of this feature using the
> ncq_prio_enable sysfs device attribute. If enabling the feature fails,
> it is because the device does not support NCQ priority. Otherwise, the
> feature is enabled and indicates that the device supports NCQ priority.
> 
> Improve this odd interface by introducing the read-only
> ncq_prio_supported sysfs device attribute to indicate if a SATA device
> supports NCQ priority. The value of this attribute reflects if the
> device flag ATA_DFLAG_NCQ_PRIO is set or cleared.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>  drivers/ata/libahci.c     |  1 +
>  drivers/ata/libata-sata.c | 24 ++++++++++++++++++++++++
>  include/linux/libata.h    |  1 +
>  3 files changed, 26 insertions(+)
> 
> diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> index fec2e9754aed..5b3fa2cbe722 100644
> --- a/drivers/ata/libahci.c
> +++ b/drivers/ata/libahci.c
> @@ -125,6 +125,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
>  struct device_attribute *ahci_sdev_attrs[] = {
>  	&dev_attr_sw_activity,
>  	&dev_attr_unload_heads,
> +	&dev_attr_ncq_prio_supported,
>  	&dev_attr_ncq_prio_enable,
>  	NULL
>  };
> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
> index dc397ebda089..5566fd4bb38f 100644
> --- a/drivers/ata/libata-sata.c
> +++ b/drivers/ata/libata-sata.c
> @@ -834,6 +834,30 @@ 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);
>  
> +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);
> +	struct ata_device *dev;
> +	bool ncq_prio_supported;
> +	int rc = 0;
> +
> +	spin_lock_irq(ap->lock);
> +	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);
> +}
> +
> +DEVICE_ATTR(ncq_prio_supported, S_IRUGO, ata_ncq_prio_supported_show, NULL);
> +EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_supported);
> +
>  static ssize_t ata_ncq_prio_enable_show(struct device *device,
>  					struct device_attribute *attr,
>  					char *buf)
> diff --git a/include/linux/libata.h b/include/linux/libata.h
> index b23f28cfc8e0..a2d1bae7900b 100644
> --- a/include/linux/libata.h
> +++ b/include/linux/libata.h
> @@ -539,6 +539,7 @@ typedef void (*ata_postreset_fn_t)(struct ata_link *link, unsigned int *classes)
>  extern struct device_attribute dev_attr_unload_heads;
>  #ifdef CONFIG_SATA_HOST
>  extern struct device_attribute dev_attr_link_power_management_policy;
> +extern struct device_attribute dev_attr_ncq_prio_supported;
>  extern struct device_attribute dev_attr_ncq_prio_enable;
>  extern struct device_attribute dev_attr_em_message_type;
>  extern struct device_attribute dev_attr_em_message;
> 
Alternative would have been to make the 'ncq_prio_enable' attribute
visible only when NCQ prio is supported, but not sure if that works out.

So:

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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