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

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

On 2021/08/06 20:37, Hannes Reinecke wrote:
> 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.

Indeed. But from the start (4.10) ncq_prio_enable is always shown, even for
devices that do not support NCQ prio. I am not sure if changing that is
acceptable as this is a user IF.

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


-- 
Damien Le Moal
Western Digital Research