[RFC 13/14] vfio/nvgrace-egm: expose the egm size through sysfs

[<ankita@nvidia.com>]

From: Ankit Agrawal <ankita@nvidia.com>

To allocate the EGM, the userspace need to know its size. Currently,
there is no easy way for the userspace to determine that.

Make nvgrace-egm expose the size through sysfs that can be queried
by the userspace from <aux_dev_path>/egm_size.

On a 2-socket, 4 GPU Grace Blackwell setup, it shows up as:
Socket0:
/sys/devices/pci0008:00/0008:00:00.0/0008:01:00.0/nvgrace_gpu_vfio_pci.egm.4/egm/egm4/egm_size
/sys/devices/pci0009:00/0009:00:00.0/0009:01:00.0/nvgrace_gpu_vfio_pci.egm.4/egm/egm4/egm_size

Socket1:
/sys/devices/pci0018:00/0018:00:00.0/0018:01:00.0/nvgrace_gpu_vfio_pci.egm.5/egm/egm5/egm_size
/sys/devices/pci0019:00/0019:00:00.0/0019:01:00.0/nvgrace_gpu_vfio_pci.egm.5/egm/egm5/egm_size

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
---
 drivers/vfio/pci/nvgrace-gpu/egm.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/vfio/pci/nvgrace-gpu/egm.c b/drivers/vfio/pci/nvgrace-gpu/egm.c
index 2cb100e39c4b..346607eeb0f9 100644
--- a/drivers/vfio/pci/nvgrace-gpu/egm.c
+++ b/drivers/vfio/pci/nvgrace-gpu/egm.c
@@ -343,6 +343,32 @@ static char *egm_devnode(const struct device *device, umode_t *mode)
 	return NULL;
 }
 
+static ssize_t egm_size_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct chardev *egm_chardev = container_of(dev, struct chardev, device);
+	struct nvgrace_egm_dev *egm_dev =
+		egm_chardev_to_nvgrace_egm_dev(egm_chardev);
+
+	return sysfs_emit(buf, "0x%lx\n", egm_dev->egmlength);
+}
+
+static DEVICE_ATTR_RO(egm_size);
+
+static struct attribute *attrs[] = {
+	&dev_attr_egm_size.attr,
+	NULL,
+};
+
+static struct attribute_group attr_group = {
+	.attrs = attrs,
+};
+
+static const struct attribute_group *attr_groups[2] = {
+	&attr_group,
+	NULL
+};
+
 static int __init nvgrace_egm_init(void)
 {
 	int ret;
@@ -364,6 +390,7 @@ static int __init nvgrace_egm_init(void)
 	}
 
 	class->devnode = egm_devnode;
+	class->dev_groups = attr_groups;
 
 	ret = auxiliary_driver_register(&egm_driver);
 	if (!ret)
-- 
2.34.1