[Nouveau] [PATCH 1/5] drm: add optional per device rwsem for all ioctls

[Marcin Slusarz]

On Mon, Apr 23, 2012 at 09:51:48AM +0200, Daniel Vetter wrote:
> On Mon, Apr 23, 2012 at 12:18:28AM +0200, Marcin Slusarz wrote:
> > Nouveau, in normal circumstances, does not need device lock for every ioctl,
> > but incoming "gpu reset" code needs exclusive access to the device.
> > This commit adds drm_driver flag which turns on read lock ioctl encapsulation.
> > 
> > Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
> 
> Why can't we just move this down to nouveau driver code?

Ok, I think it's easily possible by wrapping drm_ioctl.

> So why can't nouveau do the same? Also, if this is indeed necessary and we
> add this as some mandatory core infrastructure, it's not good enough: In
> i915 we go to great lengths to ensure that all processes waiting for gpu
> reset are still interruptible, in case the gpu reset dies unexpectedly
> (which happens), so this would need to be improved.

I came up with a scheme where down_read can be made interruptible.

I'll post both changes in a few days.

(Unfortunately adding proper down_read_interruptible / down_write_interruptible
require a bit of unfunny work - 8 architectures have their own code for rwsems)

Marcin