On Mon, Aug 10, 2015 at 02:34:18PM +0200, Thierry Reding wrote:
On Mon, Aug 10, 2015 at 02:07:49PM +0200, Daniel Vetter wrote:
On Mon, Aug 10, 2015 at 01:59:07PM +0200, Thierry Reding wrote:
On Mon, Aug 10, 2015 at 11:55:38AM +0200, Daniel Vetter wrote:
->load is depracated, bus functionst are deprecated and everyone should use drm_dev_alloc®ister.
Why would you want to deprecated ->load()? Even if you use drm_dev_alloc() and drm_dev_register(), there's still use for ->load() because it gives you the subsystem-level initialization entry point.
->load is called after the drm /dev node is registered and hence you can't really do any driver setup in there without risking races. We paper over that using drm_global_mutex, but that doesn't work for any other driver/userspace interface like sysfs/debugfs because of deadlocks.
And we can't just reorder ->load to happen before the /dev nodes are registered because a lot of drivers would fall over if we do that.
This is typical midlayer fail where the core calls into the driver instead of the other way round.
Okay, but then if we're going to deprecate ->load(), I think we should also come up with an upgrade plan. As it is, this just says that users shouldn't do ->load(), but it doesn't tell them what to do instead.
Would the proper procedure be to fix drivers so that ->load() can be called between drm_dev_alloc() and drm_dev_register()? I suppose we could add some sort of (temporary) flag for drivers to signal this and then have drm_dev_register() call ->load() at the right time. If drivers don't support it, we can keep what we have.
That, of course, doesn't get rid of the midlayer, so perhaps a better way forward would be to tell driver writers that they should be doing subsystem-level setup between drm_dev_alloc() and drm_dev_register().
That's exactly what this patch tries to accomplish by updating the kerneldoc and docbook. New sequence should be
device_probe_callback_or_whatever() { drm_dev_alloc();
... driver init code ...
drm_dev_register();
return 0; }
Unfortunately the kerneldoc markdown isn't merged yet, otherwise I'd have added this code snippet to the docs too.
Cheers, Daniel