[RFC 06/14] vfio/nvgrace-egm: Introduce egm class and register char device numbers

[<ankita@nvidia.com>]

From: Ankit Agrawal <ankita@nvidia.com>

The EGM regions are exposed to the userspace as char devices. A unique
char device with a different minor number is assigned to EGM region
belonging to a different Grace socket.

Add a new egm class and register a range of char device numbers for
the same.

Setting MAX_EGM_NODES as 4 as the 4-socket is the largest configuration
on Grace based systems.

Suggested-by: Aniket Agashe <aniketa@nvidia.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
---
 drivers/vfio/pci/nvgrace-gpu/egm.c | 36 ++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/drivers/vfio/pci/nvgrace-gpu/egm.c b/drivers/vfio/pci/nvgrace-gpu/egm.c
index 999808807019..6bab4d94cb99 100644
--- a/drivers/vfio/pci/nvgrace-gpu/egm.c
+++ b/drivers/vfio/pci/nvgrace-gpu/egm.c
@@ -4,14 +4,50 @@
  */
 
 #include <linux/vfio_pci_core.h>
+#include <linux/nvgrace-egm.h>
+
+#define MAX_EGM_NODES 4
+
+static dev_t dev;
+static struct class *class;
+
+static char *egm_devnode(const struct device *device, umode_t *mode)
+{
+	if (mode)
+		*mode = 0600;
+
+	return NULL;
+}
 
 static int __init nvgrace_egm_init(void)
 {
+	int ret;
+
+	/*
+	 * Each EGM region on a system is represented with a unique
+	 * char device with a different minor number. Allow a range
+	 * of char device creation.
+	 */
+	ret = alloc_chrdev_region(&dev, 0, MAX_EGM_NODES,
+				  NVGRACE_EGM_DEV_NAME);
+	if (ret < 0)
+		return ret;
+
+	class = class_create(NVGRACE_EGM_DEV_NAME);
+	if (IS_ERR(class)) {
+		unregister_chrdev_region(dev, MAX_EGM_NODES);
+		return PTR_ERR(class);
+	}
+
+	class->devnode = egm_devnode;
+
 	return 0;
 }
 
 static void __exit nvgrace_egm_cleanup(void)
 {
+	class_destroy(class);
+	unregister_chrdev_region(dev, MAX_EGM_NODES);
 }
 
 module_init(nvgrace_egm_init);
-- 
2.34.1