scsi: libsas: make the event threshold configurable

Add a sysfs attr that LLDD can configure it for every host. We made an
example in hisi_sas. Other LLDDs using libsas can implement it if they
want.

Suggested-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Jason Yan <[e-mail]>
CC: John Garry <[e-mail]>
CC: Johannes Thumshirn <[e-mail]>
CC: Ewan Milne <[e-mail]>
CC: Christoph Hellwig <[e-mail]>
CC: Tomas Henzl <[e-mail]>
CC: Dan Williams <[e-mail]>
Acked-by: John Garry <[e-mail]> #for hisi_sas part
Reviewed-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/hisi_sas/hisi_sas_main.c

···
 struct scsi_transport_template *hisi_sas_stt;
 EXPORT_SYMBOL_GPL(hisi_sas_stt);
 
+struct device_attribute *host_attrs[] = {
+	&dev_attr_phy_event_threshold,
+	NULL,
+};
+
 static struct scsi_host_template _hisi_sas_sht = {
 	.module			= THIS_MODULE,
 	.name			= DRV_NAME,
···
 	.eh_target_reset_handler = sas_eh_target_reset_handler,
 	.target_destroy		= sas_target_destroy,
 	.ioctl			= sas_ioctl,
+	.shost_attrs		= host_attrs,
 };
 struct scsi_host_template *hisi_sas_sht = &_hisi_sas_sht;
 EXPORT_SYMBOL_GPL(hisi_sas_sht);

drivers/scsi/libsas/sas_init.c

···
 	.smp_handler = sas_smp_handler,
 };
 
+static inline ssize_t phy_event_threshold_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct sas_ha_struct *sha = SHOST_TO_SAS_HA(shost);
+
+	return scnprintf(buf, PAGE_SIZE, "%u\n", sha->event_thres);
+}
+
+static inline ssize_t phy_event_threshold_store(struct device *dev,
+			struct device_attribute *attr,
+			const char *buf, size_t count)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct sas_ha_struct *sha = SHOST_TO_SAS_HA(shost);
+
+	sha->event_thres = simple_strtol(buf, NULL, 10);
+
+	/* threshold cannot be set too small */
+	if (sha->event_thres < 32)
+		sha->event_thres = 32;
+
+	return count;
+}
+
+DEVICE_ATTR(phy_event_threshold,
+	S_IRUGO|S_IWUSR,
+	phy_event_threshold_show,
+	phy_event_threshold_store);
+EXPORT_SYMBOL_GPL(dev_attr_phy_event_threshold);
+
 struct scsi_transport_template *
 sas_domain_attach_transport(struct sas_domain_function_template *dft)
 {

include/scsi/libsas.h

···
 			  sector_t capacity, int *hsc);
 extern struct scsi_transport_template *
 sas_domain_attach_transport(struct sas_domain_function_template *);
+extern struct device_attribute dev_attr_phy_event_threshold;
 
 int  sas_discover_root_expander(struct domain_device *);