On Tue, Mar 20, 2018 at 01:58:01PM +0200, Oleksandr Andrushchenko wrote: > On 03/19/2018 05:28 PM, Daniel Vetter wrote: > > There should be no difference between immediate removal and delayed > > removal of the drm_device from the xenbus pov. The lifetimes of the > > front-end (drm_device) and backend (the xen bus thing) are entirely > > decoupled: > Well, they are not decoupled for simplicity of handling, > please see below > > > > So for case 2 you only have 1 case: > > > > - drm_dev_unplug > > - tear down the entire xenbus backend completely > > - all xenbus access will be caught with drm_dev_entre/exit (well right > > now drm_dev_is_unplugged) checks, including any access to your private > > drm_device data > > - once drm_device->open_count == 0 the core will tear down the > > drm_device instance and call your optional drm_driver->release > > callback. > > > > So past drm_dev_unplug the drm_device is in zombie state and the only > > thing that will happen is a) it rejects all ioctls and anything else > > userspace might ask it to do and b) gets releases once the last > > userspace reference is gone. > I have re-worked the driver with this in mind [1] > So, I now use drm_dev_unplug and destroy the DRM device > on drm_driver.release. > In context of unplug work I also merged xen_drm_front_drv.c and > xen_drm_front.c as these are too coupled together now. > > Could you please take a look and tell me if this is what you mean? > > > > If the backend comes up again, you create a _new_ drm_device instance > > (while the other one is still in the process of eventually getting > > released). > We only have a single xenbus instance, so this way I'll need > to handle list of such zombies. For that reason I prefer to > wait until the DRM device is destroyed, telling the backend > to hold on until then (via going into XenbusStateReconfiguring state). Why exactly do you need to keep track of your drm_devices from the xenbus? Once unplugged, there should be no connection with the "hw" for your device, in neither direction. Maybe I need to look again, but this still smells funny and not like something you should ever do. > Another drawback of such approach is that I'll have different > minors at run-time, e.g. card0, card1, etc. > For software which has /dev/dri/card0 hardcoded it may be a problem. > But this is minor, IMO Fix userspace :-) But yeah unlikely this is a problem, hotplugging is fairly old thing. > > In short, your driver code should never have a need to look at > > drm_device->open_count. I hope this explains it a bit better. > > -Daniel > > > Yes, you are correct: at [1] I am not touching drm_device->open_count > anymore and everything just happens synchronously > [1] https://github.com/andr2000/linux/commits/drm_tip_pv_drm_v3 Please just resend, makes it easier to comment inline. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
