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SubjectRe: [patch 2a/3] Expose Power Management Policy option to users
Expose Power Management Policy option to users

This patch will modify the scsi subsystem to allow
users to set a power management policy for the link.

The scsi subsystem will create a new sysfs file for each
host in /sys/class/scsi_host called "link_power_management_policy".
This file can have 3 possible values:

Value Meaning
-------------------------------------------------------------------
min_power User wishes the link to conserve power as much as
possible, even at the cost of some performance

max_performance User wants priority to be on performance, not power
savings

medium_power User wants power savings, with less performance cost
than min_power (but less power savings as well).


Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Index: 2.6-git/drivers/scsi/hosts.c
===================================================================
--- 2.6-git.orig/drivers/scsi/hosts.c
+++ 2.6-git/drivers/scsi/hosts.c
@@ -54,6 +54,25 @@ static struct class shost_class = {
};

/**
+ * scsi_host_set_link_pm - Change the link power management policy
+ * @shost: scsi host to change the policy of.
+ * @policy: policy to change to.
+ *
+ * Returns zero if successful or an error if the requested
+ * transition is illegal.
+ **/
+int scsi_host_set_link_pm(struct Scsi_Host *shost,
+ enum scsi_host_link_pm policy)
+{
+ struct scsi_host_template *sht = shost->hostt;
+ if (sht->set_link_pm_policy)
+ sht->set_link_pm_policy(shost, policy);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(scsi_host_set_link_pm);
+
+/**
* scsi_host_set_state - Take the given host through the host
* state model.
* @shost: scsi host to change the state of.
Index: 2.6-git/drivers/scsi/scsi_sysfs.c
===================================================================
--- 2.6-git.orig/drivers/scsi/scsi_sysfs.c
+++ 2.6-git/drivers/scsi/scsi_sysfs.c
@@ -189,6 +189,74 @@ show_shost_state(struct class_device *cl

static CLASS_DEVICE_ATTR(state, S_IRUGO | S_IWUSR, show_shost_state, store_shost_state);

+static const struct {
+ enum scsi_host_link_pm value;
+ char *name;
+} shost_link_pm_policy[] = {
+ { SHOST_NOT_AVAILABLE, "max_performance" },
+ { SHOST_MIN_POWER, "min_power" },
+ { SHOST_MAX_PERFORMANCE, "max_performance" },
+ { SHOST_MEDIUM_POWER, "medium_power" },
+};
+
+const char *scsi_host_link_pm_policy(enum scsi_host_link_pm policy)
+{
+ int i;
+ char *name = NULL;
+
+ for (i = 0; i < ARRAY_SIZE(shost_link_pm_policy); i++) {
+ if (shost_link_pm_policy[i].value == policy) {
+ name = shost_link_pm_policy[i].name;
+ break;
+ }
+ }
+ return name;
+}
+
+static ssize_t store_link_pm_policy(struct class_device *class_dev,
+ const char *buf, size_t count)
+{
+ struct Scsi_Host *shost = class_to_shost(class_dev);
+ enum scsi_host_link_pm policy = 0;
+ int i;
+
+ /*
+ * we are skipping array location 0 on purpose - this
+ * is because a value of SHOST_NOT_AVAILABLE is displayed
+ * to the user as max_performance, but when the user
+ * writes "max_performance", they actually want the
+ * value to match SHOST_MAX_PERFORMANCE.
+ */
+ for (i = 1; i < ARRAY_SIZE(shost_link_pm_policy); i++) {
+ const int len = strlen(shost_link_pm_policy[i].name);
+ if (strncmp(shost_link_pm_policy[i].name, buf, len) == 0 &&
+ buf[len] == '\n') {
+ policy = shost_link_pm_policy[i].value;
+ break;
+ }
+ }
+ if (!policy)
+ return -EINVAL;
+
+ if (scsi_host_set_link_pm(shost, policy))
+ return -EINVAL;
+ return count;
+}
+static ssize_t
+show_link_pm_policy(struct class_device *class_dev, char *buf)
+{
+ struct Scsi_Host *shost = class_to_shost(class_dev);
+ const char *policy =
+ scsi_host_link_pm_policy(shost->shost_link_pm_policy);
+
+ if (!policy)
+ return -EINVAL;
+
+ return snprintf(buf, 23, "%s\n", policy);
+}
+static CLASS_DEVICE_ATTR(link_power_management_policy, S_IRUGO | S_IWUSR,
+ show_link_pm_policy, store_link_pm_policy);
+
shost_rd_attr(unique_id, "%u\n");
shost_rd_attr(host_busy, "%hu\n");
shost_rd_attr(cmd_per_lun, "%hd\n");
@@ -207,6 +275,7 @@ static struct class_device_attribute *sc
&class_device_attr_proc_name,
&class_device_attr_scan,
&class_device_attr_state,
+ &class_device_attr_link_power_management_policy,
NULL
};

Index: 2.6-git/include/scsi/scsi_host.h
===================================================================
--- 2.6-git.orig/include/scsi/scsi_host.h
+++ 2.6-git/include/scsi/scsi_host.h
@@ -42,6 +42,16 @@ enum scsi_eh_timer_return {
EH_RESET_TIMER,
};

+/*
+ * shost pm policy: If you alter this, you also need to alter scsi_sysfs.c
+ * (for the ascii descriptions)
+ */
+enum scsi_host_link_pm {
+ SHOST_NOT_AVAILABLE,
+ SHOST_MIN_POWER,
+ SHOST_MAX_PERFORMANCE,
+ SHOST_MEDIUM_POWER,
+};

struct scsi_host_template {
struct module *module;
@@ -345,6 +355,12 @@ struct scsi_host_template {
int (*suspend)(struct scsi_device *, pm_message_t state);

/*
+ * link power management support
+ */
+ int (*set_link_pm_policy)(struct Scsi_Host *, enum scsi_host_link_pm);
+ enum scsi_host_link_pm default_link_pm_policy;
+
+ /*
* Name of proc directory
*/
char *proc_name;
@@ -642,6 +658,7 @@ struct Scsi_Host {


enum scsi_host_state shost_state;
+ enum scsi_host_link_pm shost_link_pm_policy;

/* ldm bits */
struct device shost_gendev;
@@ -749,4 +766,5 @@ extern struct Scsi_Host *scsi_register(s
extern void scsi_unregister(struct Scsi_Host *);
extern int scsi_host_set_state(struct Scsi_Host *, enum scsi_host_state);

+extern int scsi_host_set_link_pm(struct Scsi_Host *, enum scsi_host_link_pm);
#endif /* _SCSI_SCSI_HOST_H */
Index: 2.6-git/Documentation/scsi/link_power_management_policy.txt
===================================================================
--- /dev/null
+++ 2.6-git/Documentation/scsi/link_power_management_policy.txt
@@ -0,0 +1,19 @@
+This parameter allows the user to set the link (interface) power management.
+There are 3 possible options:
+
+Value Effect
+----------------------------------------------------------------------------
+min_power Tell the controller to try to make the link use the
+ least possible power when possible. This may
+ sacrifice some performance due to increased latency
+ when coming out of lower power states.
+
+max_performance Generally, this means no power management. Tell
+ the controller to have performance be a priority
+ over power management.
+
+medium_power Tell the controller to enter a lower power state
+ when possible, but do not enter the lowest power
+ state, thus improving latency over min_power setting.
+
+
-
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