linux/drivers/gpu/drm/drm_usb.c
David Herrmann 099d1c290e drm: provide device-refcount
Lets not trick ourselves into thinking "drm_device" objects are not
ref-counted. That's just utterly stupid. We manage "drm_minor" objects on
each drm-device and each minor can have an unlimited number of open
handles. Each of these handles has the drm_minor (and thus the drm_device)
as private-data in the file-handle. Therefore, we may not destroy
"drm_device" until all these handles are closed.

It is *not* possible to reset all these pointers atomically and restrict
access to them, and this is *not* how this is done! Instead, we use
ref-counts to make sure the object is valid and not freed.

Note that we currently use "dev->open_count" for that, which is *exactly*
the same as a reference-count, just open coded. So this patch doesn't
change any semantics on DRM devices (well, this patch just introduces the
ref-count, anyway. Follow-up patches will replace open_count by it).

Also note that generic VFS revoke support could allow us to drop this
ref-count again. We could then just synchronously disable any fops->xy()
calls. However, this is not the case, yet, and no such patches are
in sight (and I seriously question the idea of dropping the ref-cnt
again).

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
2014-03-16 12:25:17 +01:00

85 lines
1.6 KiB
C

#include <drm/drmP.h>
#include <drm/drm_usb.h>
#include <linux/usb.h>
#include <linux/module.h>
int drm_get_usb_dev(struct usb_interface *interface,
const struct usb_device_id *id,
struct drm_driver *driver)
{
struct drm_device *dev;
int ret;
DRM_DEBUG("\n");
dev = drm_dev_alloc(driver, &interface->dev);
if (!dev)
return -ENOMEM;
dev->usbdev = interface_to_usbdev(interface);
usb_set_intfdata(interface, dev);
ret = drm_dev_register(dev, 0);
if (ret)
goto err_free;
DRM_INFO("Initialized %s %d.%d.%d %s on minor %d\n",
driver->name, driver->major, driver->minor, driver->patchlevel,
driver->date, dev->primary->index);
return 0;
err_free:
drm_dev_unref(dev);
return ret;
}
EXPORT_SYMBOL(drm_get_usb_dev);
static int drm_usb_get_irq(struct drm_device *dev)
{
return 0;
}
static const char *drm_usb_get_name(struct drm_device *dev)
{
return "USB";
}
static int drm_usb_set_busid(struct drm_device *dev,
struct drm_master *master)
{
return 0;
}
static struct drm_bus drm_usb_bus = {
.bus_type = DRIVER_BUS_USB,
.get_irq = drm_usb_get_irq,
.get_name = drm_usb_get_name,
.set_busid = drm_usb_set_busid,
};
int drm_usb_init(struct drm_driver *driver, struct usb_driver *udriver)
{
int res;
DRM_DEBUG("\n");
driver->kdriver.usb = udriver;
driver->bus = &drm_usb_bus;
res = usb_register(udriver);
return res;
}
EXPORT_SYMBOL(drm_usb_init);
void drm_usb_exit(struct drm_driver *driver,
struct usb_driver *udriver)
{
usb_deregister(udriver);
}
EXPORT_SYMBOL(drm_usb_exit);
MODULE_AUTHOR("David Airlie");
MODULE_DESCRIPTION("USB DRM support");
MODULE_LICENSE("GPL and additional rights");