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Date: Thu, 7 Mar 2024 10:51:37 +0100
From: Niklas Cassel <cassel@kernel.org>
To: Igor Pylypiv <ipylypiv@google.com>
Cc: Damien Le Moal <dlemoal@kernel.org>, Hannes Reinecke <hare@suse.de>,
	John Garry <john.g.garry@oracle.com>,
	Jason Yan <yanaijie@huawei.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Jack Wang <jinpu.wang@cloud.ionos.com>,
	Xiang Chen <chenxiang66@hisilicon.com>,
	Artur Paszkiewicz <artur.paszkiewicz@intel.com>,
	Bart Van Assche <bvanassche@acm.org>,
	TJ Adams <tadamsjr@google.com>, linux-ide@vger.kernel.org,
	linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 2/7] scsi: libsas: Define NCQ Priority sysfs
 attributes for SATA devices
Message-ID: <ZemOKZAWuIY1hcpU@ryzen>
References: <20240306012226.3398927-1-ipylypiv@google.com>
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 <ZehLfEjfOTs2wGZe@ryzen>
 <ZejD6mYBhYFQ5Xq8@google.com>
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On Wed, Mar 06, 2024 at 11:28:42AM -0800, Igor Pylypiv wrote:
> On Wed, Mar 06, 2024 at 11:54:52AM +0100, Niklas Cassel wrote:
> > On Tue, Mar 05, 2024 at 05:22:21PM -0800, Igor Pylypiv wrote:
> > > Libata sysfs attributes cannot be used for libsas managed SATA devices
> > > because the ata_port location is different for libsas.
> > > 
> > > Defined sysfs attributes (visible for SATA devices only):
> > > - /sys/block/sda/device/ncq_prio_enable
> > > - /sys/block/sda/device/ncq_prio_supported
> > > 
> > > The newly defined attributes will pass the correct ata_port to libata
> > > helper functions.
> > > 
> > > Reviewed-by: John Garry <john.g.garry@oracle.com>
> > > Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> > > Reviewed-by: Jason Yan <yanaijie@huawei.com>
> > > Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
> > > ---
> > >  drivers/scsi/libsas/sas_ata.c | 94 +++++++++++++++++++++++++++++++++++
> > >  include/scsi/sas_ata.h        |  6 +++
> > >  2 files changed, 100 insertions(+)
> > > 
> > > diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
> > > index 12e2653846e3..04b0bd9a4e01 100644
> > > --- a/drivers/scsi/libsas/sas_ata.c
> > > +++ b/drivers/scsi/libsas/sas_ata.c
> > > @@ -964,3 +964,97 @@ int sas_execute_ata_cmd(struct domain_device *device, u8 *fis, int force_phy_id)
> > >  			       force_phy_id, &tmf_task);
> > >  }
> > >  EXPORT_SYMBOL_GPL(sas_execute_ata_cmd);
> > > +
> > > +static ssize_t sas_ncq_prio_supported_show(struct device *device,
> > > +					   struct device_attribute *attr,
> > > +					   char *buf)
> > > +{
> > > +	struct scsi_device *sdev = to_scsi_device(device);
> > > +	struct domain_device *ddev = sdev_to_domain_dev(sdev);
> > > +	bool supported;
> > > +	int rc;
> > > +
> > > +	/* This attribute shall be visible for SATA devices only */
> > > +	if (WARN_ON_ONCE(!dev_is_sata(ddev)))
> > > +		return -EINVAL;
> > 
> > Like Hannes commented, I don't believe this is needed.
> > 
> 
> The intention for the check is to serve as a fail-safe in case 'is_visible()'
> callback gets incorrectly modified and stops hiding the sysfs attributes
> for non-SATA devices.
> 
> Just want to clarify should I remove the WARN_ON_ONCE and keep the fail-safe
> check or should I get rid of the check completely and trust 'is_visible()'
> to always hide the sysfs attributes for non-SATA devices?

I think that you can remove both the WARN_ON_ONCE and the
if (!dev_is_sata()).

We usually don't keep code around "just in case someone modifies some
other function sometime in the future".


If someone changes is_visible() to remove the dev_is_sata() check,
then they would introuce a bug. I don't see why anyone would change that,
but if someone tried to remove that check from is_visible() anyway,
I'm assuming that someone would catch it during code review.


> 
> > 
> > > +
> > > +	rc = ata_ncq_prio_supported(ddev->sata_dev.ap, sdev, &supported);
> > > +	if (rc)
> > > +		return rc;
> > > +
> > > +	return sysfs_emit(buf, "%d\n", supported);
> > > +}
> > > +
> > 
> > While this is a bit different depending on file, the most common way is to
> > have no blank link before the DEVICE_ATTR().
> >
> 
> In "[PATCH 1/3] ata: libata-sata: Factor out NCQ Priority configuration helpers"
> Damien asked to keep the blank link before the DEVICE_ATTR() in libata-sata.c.
> 
> Non-prio sysfs attributes in libata-sata.c don't have blank lines
> before DEVICE_ATTR() so I'm more inclined to remove the lines.
> 
> I'm fine with either of ways, just want to get a consensus and make it 
> consistent for both libata-sata.c and sas_ata.c.

While it is a bit different depending on file, it is slightly more common
to no have a extra blank line before DEVICE_ATTR():

$ git grep -B 1 DEVICE_ATTR | grep "}" | wc -l
2167

$ git grep -B 1 DEVICE_ATTR | grep -- "c-$" | wc -l
1725

But I'm fine to keep it like it is, especially if Damien already had expresed
a preference.


Kind regards,
Niklas

>  
> > 
> > > +DEVICE_ATTR(ncq_prio_supported, S_IRUGO, sas_ncq_prio_supported_show, NULL);
> > > +
> > > +static ssize_t sas_ncq_prio_enable_show(struct device *device,
> > > +					struct device_attribute *attr,
> > > +					char *buf)
> > > +{
> > > +	struct scsi_device *sdev = to_scsi_device(device);
> > > +	struct domain_device *ddev = sdev_to_domain_dev(sdev);
> > > +	bool enabled;
> > > +	int rc;
> > > +
> > > +	/* This attribute shall be visible for SATA devices only */
> > > +	if (WARN_ON_ONCE(!dev_is_sata(ddev)))
> > > +		return -EINVAL;
> > > +
> > > +	rc = ata_ncq_prio_enabled(ddev->sata_dev.ap, sdev, &enabled);
> > > +	if (rc)
> > > +		return rc;
> > > +
> > > +	return sysfs_emit(buf, "%d\n", enabled);
> > > +}
> > > +
> > > +static ssize_t sas_ncq_prio_enable_store(struct device *device,
> > > +					 struct device_attribute *attr,
> > > +					 const char *buf, size_t len)
> > > +{
> > > +	struct scsi_device *sdev = to_scsi_device(device);
> > > +	struct domain_device *ddev = sdev_to_domain_dev(sdev);
> > > +	bool enable;
> > > +	int rc;
> > > +
> > > +	/* This attribute shall be visible for SATA devices only */
> > > +	if (WARN_ON_ONCE(!dev_is_sata(ddev)))
> > > +		return -EINVAL;
> > > +
> > > +	rc = kstrtobool(buf, &enable);
> > > +	if (rc)
> > > +		return rc;
> > > +
> > > +	rc = ata_ncq_prio_enable(ddev->sata_dev.ap, sdev, enable);
> > > +	if (rc)
> > > +		return rc;
> > > +
> > > +	return len;
> > > +}
> > > +
> > > +DEVICE_ATTR(ncq_prio_enable, S_IRUGO | S_IWUSR,
> > > +	    sas_ncq_prio_enable_show, sas_ncq_prio_enable_store);
> > > +
> > > +static struct attribute *sas_ata_sdev_attrs[] = {
> > > +	&dev_attr_ncq_prio_supported.attr,
> > > +	&dev_attr_ncq_prio_enable.attr,
> > > +	NULL
> > > +};
> > > +
> > > +static umode_t sas_ata_attr_is_visible(struct kobject *kobj,
> > > +				       struct attribute *attr, int i)
> > > +{
> > > +	struct device *dev = kobj_to_dev(kobj);
> > > +	struct scsi_device *sdev = to_scsi_device(dev);
> > > +	struct domain_device *ddev = sdev_to_domain_dev(sdev);
> > > +
> > > +	if (!dev_is_sata(ddev))
> > > +		return 0;
> > > +
> > > +	return attr->mode;
> > > +}
> > > +
> > > +const struct attribute_group sas_ata_sdev_attr_group = {
> > > +	.attrs = sas_ata_sdev_attrs,
> > > +	.is_visible = sas_ata_attr_is_visible,
> > > +};
> > > +EXPORT_SYMBOL_GPL(sas_ata_sdev_attr_group);
> > > diff --git a/include/scsi/sas_ata.h b/include/scsi/sas_ata.h
> > > index 2f8c719840a6..92e27e7bf088 100644
> > > --- a/include/scsi/sas_ata.h
> > > +++ b/include/scsi/sas_ata.h
> > > @@ -39,6 +39,9 @@ int smp_ata_check_ready_type(struct ata_link *link);
> > >  int sas_discover_sata(struct domain_device *dev);
> > >  int sas_ata_add_dev(struct domain_device *parent, struct ex_phy *phy,
> > >  		    struct domain_device *child, int phy_id);
> > > +
> > > +extern const struct attribute_group sas_ata_sdev_attr_group;
> > > +
> > >  #else
> > >  
> > >  static inline void sas_ata_disabled_notice(void)
> > > @@ -123,6 +126,9 @@ static inline int sas_ata_add_dev(struct domain_device *parent, struct ex_phy *p
> > >  	sas_ata_disabled_notice();
> > >  	return -ENODEV;
> > >  }
> > > +
> > > +#define sas_ata_sdev_attr_group ((struct attribute_group) {})
> > > +
> > >  #endif
> > >  
> > >  #endif /* _SAS_ATA_H_ */
> > > -- 
> > > 2.44.0.278.ge034bb2e1d-goog
> > >