Re: [PATCH v2 9/9] scsi: mpt3sas: Introduce sas_ncq_prio_supported sysfs sttribute

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/08/06 18:12, Hannes Reinecke wrote:
> On 8/6/21 9:42 AM, Damien Le Moal wrote:
>> Similarly to AHCI, introduce the device sysfs attribute
>> sas_ncq_prio_supported to advertize if a SATA device supports the NCQ
>> priority feature. Without this new attribute, the user can only
>> discover if a SATA device supports NCQ priority by trying to enable
>> the feature use with the sas_ncq_prio_enable sysfs device attribute,
>> which fails when the device does not support high priroity commands.
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>>  drivers/scsi/mpt3sas/mpt3sas_ctl.c | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/drivers/scsi/mpt3sas/mpt3sas_ctl.c b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> index b66140e4c370..f83d4d32d459 100644
>> --- a/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> +++ b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> @@ -3918,6 +3918,24 @@ sas_device_handle_show(struct device *dev, struct device_attribute *attr,
>>  }
>>  static DEVICE_ATTR_RO(sas_device_handle);
>>  
>> +/**
>> + * sas_ncq_prio_supported_show - Indicate if device supports NCQ priority
>> + * @dev: pointer to embedded device
>> + * @attr: sas_ncq_prio_supported attribute descriptor
>> + * @buf: the buffer returned
>> + *
>> + * A sysfs 'read-only' sdev attribute, only works with SATA
>> + */
>> +static ssize_t
>> +sas_ncq_prio_supported_show(struct device *dev,
>> +			    struct device_attribute *attr, char *buf)
>> +{
>> +	struct scsi_device *sdev = to_scsi_device(dev);
>> +
>> +	return sysfs_emit(buf, "%d\n", scsih_ncq_prio_supp(sdev));
>> +}
>> +static DEVICE_ATTR_RO(sas_ncq_prio_supported);
>> +
>>  /**
>>   * sas_ncq_prio_enable_show - send prioritized io commands to device
>>   * @dev: pointer to embedded device
>> @@ -3960,6 +3978,7 @@ static DEVICE_ATTR_RW(sas_ncq_prio_enable);
>>  struct device_attribute *mpt3sas_dev_attrs[] = {
>>  	&dev_attr_sas_address,
>>  	&dev_attr_sas_device_handle,
>> +	&dev_attr_sas_ncq_prio_supported,
>>  	&dev_attr_sas_ncq_prio_enable,
>>  	NULL,
>>  };
>>
> One wonders where the relationship to the previous patches are, but hey:

Yes, hard to see... mpt3sas is the only SAS HBA that can actually carry the
"high prio" bit for the command to the HBA FW SATL using the prio bit of the SAS
frame for the SCSI command that is to be translated into a high prio SATA command.

This driver supports NCQ priority since the first support series in 4.10 kernel.
So I added the same change as for libahci to keep it in sync with the pure ATA
side of things.

But sure, it could be a patch on its own outside this series.

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


-- 
Damien Le Moal
Western Digital Research