[PATCH 4/5] drm: Add support for subclassing struct drm_device

[Damien Lespiau <damien.lespiau@intel.com>]

Currently, drivers are expected to allocate private data and attach it
to dev_private in struct drm_device.

This has the unfortunate property to require driver code to juggle
between the pointer to struct drm_device and dev->dev_private instead of
using the same pointer if they could embed the device structure.

This patch enables drivers to declare the size of the device structure
they want DRM core to create for them.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
---
 drivers/gpu/drm/drm_stub.c | 8 +++++++-
 include/drm/drmP.h         | 8 ++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index 98a33c580..161dd9a 100644
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -433,8 +433,14 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 {
 	struct drm_device *dev;
 	int ret;
+	size_t device_struct_size;
 
-	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (driver->device_struct_size)
+		device_struct_size = driver->device_struct_size;
+	else
+		device_struct_size = sizeof(*dev);
+
+	dev = kzalloc(device_struct_size, GFP_KERNEL);
 	if (!dev)
 		return NULL;
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 6800c20..219b153 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -996,6 +996,14 @@ struct drm_driver {
 	u32 driver_features;
 	/* size of the private data attached to a struct drm_buf */
 	int buf_priv_size;
+	/*
+	 * DRM drivers can subclass struct drm_device to have their own device
+	 * structure to store private data. In this case, they need to declare
+	 * the size of the child structure (ie the structure embedding a struct
+	 * drm_device as first field) for the DRM core to allocate a big
+	 * enough device structure.
+	 */
+	size_t device_struct_size;
 	const struct drm_ioctl_desc *ioctls;
 	int num_ioctls;
 	const struct file_operations *fops;
-- 
1.8.3.1