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Subject[PATCH 3/8] dax: register seed device
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Date
Towards adding support for sub-dividing device-dax regions, add a seed
device. Similar to libnvdimm a 'seed' device is un-configured device
that is enabled after setting configuration parameters. After a given
seed device is enabled another is created and this process repeats until
no more seed devices can be activated due to dax_available_size being
exhausted.

For now, this simply registers a seed instance after the first dax
device instance is established.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/dax.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index da2962b6f8de..c9ba011e333b 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -40,8 +40,10 @@ MODULE_PARM_DESC(nr_dax, "max number of device-dax instances");
* @kref: to pin while other agents have a need to do lookups
* @lock: synchronize changes / consistent-access to the resource tree (@res)
* @dev: parent device backing this region
+ * @seed: next device for dynamic allocation / configuration
* @align: allocation and mapping alignment for child dax devices
* @res: physical address range of the region
+ * @child_count: number of registered dax device instances
* @pfn_flags: identify whether the pfns are paged back or not
*/
struct dax_region {
@@ -51,8 +53,10 @@ struct dax_region {
struct kref kref;
struct mutex lock;
struct device *dev;
+ struct device *seed;
unsigned int align;
struct resource res;
+ atomic_t child_count;
unsigned long pfn_flags;
};

@@ -161,10 +165,31 @@ static ssize_t align_show(struct device *dev,
}
static DEVICE_ATTR_RO(align);

+static ssize_t seed_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct dax_region *dax_region;
+ ssize_t rc = -ENXIO;
+
+ device_lock(dev);
+ dax_region = dev_get_drvdata(dev);
+ if (dax_region) {
+ mutex_lock(&dax_region->lock);
+ if (dax_region->seed)
+ rc = sprintf(buf, "%s\n", dev_name(dax_region->seed));
+ mutex_unlock(&dax_region->lock);
+ }
+ device_unlock(dev);
+
+ return rc;
+}
+static DEVICE_ATTR_RO(seed);
+
static struct attribute *dax_region_attributes[] = {
&dev_attr_available_size.attr,
&dev_attr_region_size.attr,
&dev_attr_align.attr,
+ &dev_attr_seed.attr,
&dev_attr_id.attr,
NULL,
};
@@ -295,6 +320,9 @@ static void dax_region_free(struct kref *kref)
struct dax_region *dax_region;

dax_region = container_of(kref, struct dax_region, kref);
+ WARN(atomic_read(&dax_region->child_count),
+ "%s: child count not zero\n",
+ dev_name(dax_region->dev));
kfree(dax_region);
}

@@ -691,7 +719,10 @@ static void unregister_dax_dev(void *dev)
for (i = 0; i < dax_dev->num_resources; i++)
__release_region(&dax_region->res, dax_dev->res[i]->start,
resource_size(dax_dev->res[i]));
+ if (dax_region->seed == dev)
+ dax_region->seed = NULL;
mutex_unlock(&dax_region->lock);
+ atomic_dec(&dax_region->child_count);

cdev_del(cdev);
device_unregister(dev);
@@ -796,6 +827,16 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
if (rc)
return ERR_PTR(rc);

+ if (atomic_inc_return(&dax_region->child_count) == 1) {
+ struct dax_dev *seed;
+
+ seed = devm_create_dax_dev(dax_region, NULL, 0);
+ if (IS_ERR(seed))
+ dev_warn(parent, "failed to create region seed\n");
+ else
+ dax_region->seed = &seed->dev;
+ }
+
return dax_dev;

err_cdev:
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