On Tue, Feb 14, 2023 at 10:28:24AM +0100, Christian König wrote: > Am 14.02.23 um 09:59 schrieb Stanislaw Gruszka: > > On Thu, Feb 09, 2023 at 09:18:35AM +0100, Christian König wrote: > > > Hello everyone, > > > > > > the drm_debugfs has a couple of well known design problems. > > > > > > Especially it wasn't possible to add files between initializing and registering > > > of DRM devices since the underlying debugfs directory wasn't created yet. > > > > > > The resulting necessity of the driver->debugfs_init() callback function is a > > > mid-layering which is really frowned on since it creates a horrible > > > driver->DRM->driver design layering. > > > > > > The recent patch "drm/debugfs: create device-centered debugfs functions" tried > > > to address those problem, but doesn't seem to work correctly. This looks like > > > a misunderstanding of the call flow around drm_debugfs_init(), which is called > > > multiple times, once for the primary and once for the render node. > > > > > > So what happens now is the following: > > > > > > 1. drm_dev_init() initially allocates the drm_minor objects. > > > 2. ... back to the driver ... > > > 3. drm_dev_register() is called. > > > > > > 4. drm_debugfs_init() is called for the primary node. > > > 5. drm_framebuffer_debugfs_init(), drm_client_debugfs_init() and > > > drm_atomic_debugfs_init() call drm_debugfs_add_file(s)() to add the files > > > for the primary node. > > > 6. The driver->debugfs_init() callback is called to add debugfs files for the > > > primary node. > > > 7. The added files are consumed and added to the primary node debugfs directory. > > > > > > 8. drm_debugfs_init() is called for the render node. > > > 9. drm_framebuffer_debugfs_init(), drm_client_debugfs_init() and > > > drm_atomic_debugfs_init() call drm_debugfs_add_file(s)() to add the files > > > again for the render node. > > > 10. The driver->debugfs_init() callback is called to add debugfs files for the > > > render node. > > > 11. The added files are consumed and added to the render node debugfs directory. > > > > > > 12. Some more files are added through drm_debugfs_add_file(). > > > 13. drm_debugfs_late_register() add the files once more to the primary node > > > debugfs directory. > > > 14. From this point on files added through drm_debugfs_add_file() are simply ignored. > > > 15. ... back to the driver ... > > > > > > Because of this the dev->debugfs_mutex lock is also completely pointless since > > > any concurrent use of the interface would just randomly either add the files to > > > the primary or render node or just not at all. > > > > > > Even worse is that this implementation nails the coffin for removing the > > > driver->debugfs_init() mid-layering because otherwise drivers can't control > > > where their debugfs (primary/render node) are actually added. > > > > > > This patch set here now tries to clean this up a bit, but most likely isn't > > > fully complete either since I didn't audit every driver/call path. > > > > > > Please comment/discuss. > > What is end goal here regarding debugfs in DRM ? My undersigning is that > > the direction is get rid of debugfs_init callback as described in: > > https://cgit.freedesktop.org/drm/drm-misc/tree/Documentation/gpu/todo.rst#n511 > > and also make it driver/device-centric instead of minor-centric as > > described here: > > https://cgit.freedesktop.org/drm/drm-misc/commit/?id=99845faae7099cd704ebf67514c1157c26960a > > Well my main goal is to get rid of the debugfs_init() mid-layering in the > mid term, everything else is just nice to have. > > > I'm asking from accel point of view. We can make things there as they > > should look like at the end for DRM, since currently no drivers have > > established their interfaces and they can be changed. > > > > Is drivers/device-centric mean we should use drm_dev->unique for debugfs > > dir entry name instead of minor ? > > Oh, good idea! That would also finally make it a bit less problematic to > figure out which PCI or platform device corresponds to which debugfs > directory. > > Only potential problem I see is that we would need to rename the directory > should a driver every decide to set drm_dev->unique to something else than > the default. But a quick check shows no users of drm_dev_set_unique(), so we > could potentially just unexport the function > > > Or perhaps we should have 2 separate dir entries: one (old dri/minor/) > > for device drm debugfs files and other one for driver specific files ? > > How about we just create symlinks between the old and the new directory for > now which we remove after everything has settled again? Yes, that would make perfect sense. However my idea was a bit different, that we have separate directories one for drm specific debugfs files (i.e. clints, framebuffer, gem, ... ) and another one for driver specific files (registers, whatever individual needs for debugging). I'm just considering different options. > > Also what regarding sysfs ? Should we do something with accel_sysfs_device_minor ? > > I see sysfs as a different and probably even more complicated topic. I wish to have some clear guidance how things should be done regarding sysfs. But I guess we can stick with accel_sysfs_device_minor for accel as it is currently. And make changes along with whole DRM. Regards Stanislaw
