[HMM v14 16/16] mm/hmm/devmem: dummy HMM device as an helper for ZONE_DEVICE memory

["Jérôme Glisse" <jglisse@redhat.com>]

This introduce a dummy HMM device class so device driver can use it to
create hmm_device for the sole purpose of registering device memory.
It is usefull to device driver that want to manage multiple physical
device memory under same device umbrella.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Evgeny Baskakov <ebaskakov@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: Sherry Cheung <SCheung@nvidia.com>
Signed-off-by: Subhash Gutti <sgutti@nvidia.com>
---
 include/linux/hmm.h | 22 ++++++++++++-
 mm/hmm.c            | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 116 insertions(+), 1 deletion(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 674aa79..57e88e4 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -76,10 +76,10 @@
 
 #if IS_ENABLED(CONFIG_HMM)
 
+#include <linux/device.h>
 #include <linux/memremap.h>
 #include <linux/completion.h>
 
-
 struct hmm;
 
 /*
@@ -490,6 +490,26 @@ static inline unsigned long hmm_devmem_page_get_drvdata(struct page *page)
 
 	return drvdata[1];
 }
+
+
+/*
+ * struct hmm_device - fake device to hang device memory onto
+ *
+ * @device: device struct
+ * @minor: device minor number
+ */
+struct hmm_device {
+	struct device		device;
+	unsigned		minor;
+};
+
+/*
+ * Device driver that want to handle multiple devices memory through a single
+ * fake device can use hmm_device to do so. This is purely an helper and it
+ * is not needed to make use of any HMM functionality.
+ */
+struct hmm_device *hmm_device_new(void);
+void hmm_device_put(struct hmm_device *hmm_device);
 #endif /* IS_ENABLED(CONFIG_HMM_DEVMEM) */
 
 
diff --git a/mm/hmm.c b/mm/hmm.c
index 4d3b399..df25810 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/mmzone.h>
+#include <linux/module.h>
 #include <linux/pagemap.h>
 #include <linux/swapops.h>
 #include <linux/hugetlb.h>
@@ -984,4 +985,98 @@ int hmm_devmem_fault_range(struct hmm_devmem *devmem,
 	return 0;
 }
 EXPORT_SYMBOL(hmm_devmem_fault_range);
+
+/*
+ * Device driver that want to handle multiple devices memory through a single
+ * fake device can use hmm_device to do so. This is purely an helper and it
+ * is not needed to make use of any HMM functionality.
+ */
+#define HMM_DEVICE_MAX 256
+
+static DECLARE_BITMAP(hmm_device_mask, HMM_DEVICE_MAX);
+static DEFINE_SPINLOCK(hmm_device_lock);
+static struct class *hmm_device_class;
+static dev_t hmm_device_devt;
+
+static void hmm_device_release(struct device *device)
+{
+	struct hmm_device *hmm_device;
+
+	hmm_device = container_of(device, struct hmm_device, device);
+	spin_lock(&hmm_device_lock);
+	clear_bit(hmm_device->minor, hmm_device_mask);
+	spin_unlock(&hmm_device_lock);
+
+	kfree(hmm_device);
+}
+
+struct hmm_device *hmm_device_new(void)
+{
+	struct hmm_device *hmm_device;
+	int ret;
+
+	hmm_device = kzalloc(sizeof(*hmm_device), GFP_KERNEL);
+	if (!hmm_device)
+		return ERR_PTR(-ENOMEM);
+
+	ret = alloc_chrdev_region(&hmm_device->device.devt,0,1,"hmm_device");
+	if (ret < 0) {
+		kfree(hmm_device);
+		return NULL;
+	}
+
+	spin_lock(&hmm_device_lock);
+	hmm_device->minor=find_first_zero_bit(hmm_device_mask,HMM_DEVICE_MAX);
+	if (hmm_device->minor >= HMM_DEVICE_MAX) {
+		spin_unlock(&hmm_device_lock);
+		kfree(hmm_device);
+		return NULL;
+	}
+	set_bit(hmm_device->minor, hmm_device_mask);
+	spin_unlock(&hmm_device_lock);
+
+	dev_set_name(&hmm_device->device, "hmm_device%d", hmm_device->minor);
+	hmm_device->device.devt = MKDEV(MAJOR(hmm_device_devt),
+					hmm_device->minor);
+	hmm_device->device.release = hmm_device_release;
+	hmm_device->device.class = hmm_device_class;
+	device_initialize(&hmm_device->device);
+
+	return hmm_device;
+}
+EXPORT_SYMBOL(hmm_device_new);
+
+void hmm_device_put(struct hmm_device *hmm_device)
+{
+	put_device(&hmm_device->device);
+}
+EXPORT_SYMBOL(hmm_device_put);
+
+static int __init hmm_init(void)
+{
+	int ret;
+
+	ret = alloc_chrdev_region(&hmm_device_devt, 0,
+				  HMM_DEVICE_MAX,
+				  "hmm_device");
+	if (ret)
+		return ret;
+
+	hmm_device_class = class_create(THIS_MODULE, "hmm_device");
+	if (IS_ERR(hmm_device_class)) {
+		unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
+		return PTR_ERR(hmm_device_class);
+	}
+	return 0;
+}
+
+static void __exit hmm_exit(void)
+{
+	unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
+	class_destroy(hmm_device_class);
+}
+
+module_init(hmm_init);
+module_exit(hmm_exit);
+MODULE_LICENSE("GPL");
 #endif /* IS_ENABLED(CONFIG_HMM_DEVMEM) */
-- 
2.4.3