[HMM v17 14/14] mm/hmm/devmem: dummy HMM device for ZONE_DEVICE memory v2

["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 struct device umbrella.

Changed since v1:
  - Improve commit message
  - Add drvdata parameter to set on struct device

Signed-off-by: JA(C)rA'me 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            | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+), 1 deletion(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 2332f89..5528081 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -76,11 +76,11 @@
 
 #if IS_ENABLED(CONFIG_HMM)
 
+#include <linux/device.h>
 #include <linux/migrate.h>
 #include <linux/memremap.h>
 #include <linux/completion.h>
 
-
 struct hmm;
 
 /*
@@ -429,6 +429,26 @@ 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 *drvdata);
+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 61a8c24..41f11f2 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>
@@ -1136,4 +1137,99 @@ 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 *drvdata)
+{
+	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;
+	dev_set_drvdata(&hmm_device->device, drvdata);
+	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

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