Re: [PATCH] regulator: userspace-consumer: Add regulator event support

From: Zev Weiss
Date: Thu Aug 03 2023 - 16:52:52 EST


On Thu, Aug 03, 2023 at 04:12:25AM PDT, Naresh Solanki wrote:
Add sysfs attribute to track regulator events received from regulator
notifier block handler.


Hi Naresh,

Could you provide a bit more detail on how this is intended to be used? Some of the details (more below) seem a bit odd to me...

Signed-off-by: Naresh Solanki <Naresh.Solanki@xxxxxxxxxxxxx>
---
drivers/regulator/userspace-consumer.c | 52 +++++++++++++++++++++++++-
1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/drivers/regulator/userspace-consumer.c b/drivers/regulator/userspace-consumer.c
index 97f075ed68c9..a0b980022993 100644
--- a/drivers/regulator/userspace-consumer.c
+++ b/drivers/regulator/userspace-consumer.c
@@ -29,6 +29,10 @@ struct userspace_consumer_data {

int num_supplies;
struct regulator_bulk_data *supplies;
+
+ struct kobject *kobj;
+ struct notifier_block nb;
+ unsigned long events;
};

static ssize_t name_show(struct device *dev,
@@ -89,12 +93,30 @@ static ssize_t state_store(struct device *dev, struct device_attribute *attr,
return count;
}

+static DEFINE_MUTEX(events_lock);
+
+static ssize_t events_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct userspace_consumer_data *data = dev_get_drvdata(dev);
+ unsigned long e;
+
+ mutex_lock(&events_lock);
+ e = data->events;
+ data->events = 0;

...particularly this bit -- a read operation on a read-only file (and especially one with 0644 permissions) having side-effects (clearing the value it accesses) seems on the face of it like fairly surprising behavior. Is this a pattern that's used elsewhere in any other sysfs files?

+ mutex_unlock(&events_lock);
+
+ return sprintf(buf, "0x%lx\n", e);
+}
+
static DEVICE_ATTR_RO(name);
static DEVICE_ATTR_RW(state);
+static DEVICE_ATTR_RO(events);

New sysfs attributes should be documented in Documentation/ABI, which this appears to be missing.

However, it looks like this would expose the values of all the REGULATOR_EVENT_* constants as a userspace-visible ABI -- is that something we really want to do?


static struct attribute *attributes[] = {
&dev_attr_name.attr,
&dev_attr_state.attr,
+ &dev_attr_events.attr,
NULL,
};

@@ -115,12 +137,28 @@ static const struct attribute_group attr_group = {
.is_visible = attr_visible,
};

+static int regulator_userspace_notify(struct notifier_block *nb,
+ unsigned long event,
+ void *ignored)
+{
+ struct userspace_consumer_data *data =
+ container_of(nb, struct userspace_consumer_data, nb);
+
+ mutex_lock(&events_lock);
+ data->events |= event;
+ mutex_unlock(&events_lock);
+

Using a single global mutex (events_lock) to protect a single member of a per-device struct looks weird. Unless there's something subtle going on that I'm not seeing, it seems like the lock should be a member of the data struct instead of global, and since no blocking operations happen under it could it just be a spinlock? Or since it's just some simple updates to a single variable, why not just use an atomic_t and skip the lock entirely?

+ sysfs_notify(data->kobj, NULL, dev_attr_events.attr.name);
+
+ return NOTIFY_OK;
+}
+
static int regulator_userspace_consumer_probe(struct platform_device *pdev)
{
struct regulator_userspace_consumer_data tmpdata;
struct regulator_userspace_consumer_data *pdata;
struct userspace_consumer_data *drvdata;
- int ret;
+ int i, ret;

pdata = dev_get_platdata(&pdev->dev);
if (!pdata) {
@@ -153,6 +191,7 @@ static int regulator_userspace_consumer_probe(struct platform_device *pdev)
drvdata->num_supplies = pdata->num_supplies;
drvdata->supplies = pdata->supplies;
drvdata->no_autoswitch = pdata->no_autoswitch;
+ drvdata->kobj = &pdev->dev.kobj;

mutex_init(&drvdata->lock);

@@ -186,6 +225,13 @@ static int regulator_userspace_consumer_probe(struct platform_device *pdev)
}
drvdata->enabled = !!ret;

+ drvdata->nb.notifier_call = regulator_userspace_notify;
+ for (i = 0; i < drvdata->num_supplies; i++) {
+ ret = devm_regulator_register_notifier(drvdata->supplies[i].consumer, &drvdata->nb);
+ if (ret)
+ goto err_enable;
+ }
+
return 0;

err_enable:
@@ -197,6 +243,10 @@ static int regulator_userspace_consumer_probe(struct platform_device *pdev)
static int regulator_userspace_consumer_remove(struct platform_device *pdev)
{
struct userspace_consumer_data *data = platform_get_drvdata(pdev);
+ int i;
+
+ for (i = 0; i < data->num_supplies; i++)
+ devm_regulator_unregister_notifier(data->supplies[i].consumer, &data->nb);

sysfs_remove_group(&pdev->dev.kobj, &attr_group);


base-commit: 4fb53b2377c364e3753d6e293913b57dad68e98b
--
2.41.0