Hi Swati, On Monday 19 Dec 2016 16:12:22 swati.dhingra@xxxxxxxxx wrote: > From: Swati Dhingra <swati.dhingra@xxxxxxxxx> > > Currently, we don't have a stable ABI which can be used for the purpose of > providing output debug/loggging/crc and other such data from DRM. > The ABI in current use (filesystems, ioctls, et al.) have their own > constraints and are intended to output a particular type of data. > Few cases in point: > sysfs - stable ABI, but constrained to one textual value per file > debugfs - unstable ABI, free-for-all > ioctls - not as suitable to many single purpose continuous data > dumping, we would very quickly run out ioctl space; requires more > userspace support than "cat" > device nodes - a real possibilty, kernel instantiation is more tricky, > requires udev (+udev.rules) or userspace discovery of the > dynamic major:minor (via sysfs) [mounting a registered > filesystem is easy in comparison] > netlink - stream based, therefore involves numerous copies. > > Debugfs is the lesser among the evils here, thereby we have grown used to > the convenience and flexibility in presentation that debugfs gives us > (including relayfs inodes) that we want some of that hierachy in stable user > ABI form. Seriously, why ? A subsystem growing its own file system sounds so wrong. It seems that you want to have all the benefits of a stable ABI without going through the standardization effort that this requires. I can see so many ways that drmfs could be abused, with drivers throwing in new data with little or no review. You'll need very compelling arguments to convince me. > Due to these limitations, there is a need for a new pseudo filesytem, that > would act as a stable 'free-for-all' ABI, with the heirarchial structure and > thus convenience of debugfs. This will be managed by drm, thus named > 'drmfs'. DRM would register this filesystem to manage a canonical > mountpoint, but this wouldn't limit everyone to only using that pseudofs > underneath. > > This can serve to hold various kinds of output data from Linux DRM > subsystems, for the files which can't truely fit anywhere else with > existing ABI's but present so, for the lack of a better place. > > In this patch series, we have introduced a pseudo filesystem named as > 'drmfs' for now. The filesystem is introduced in the first patch, and the > subsequent patches make use of the filesystem interfaces, in drm driver, > and making them available for use by the drm subsystem components, one of > which is i915. We've moved the location of i915 GuC logs from debugfs to > drmfs in the last patch. Subsequently, more such files such as pipe_crc, > error states, memory stats, etc. can be move to this filesystem, if the > idea introduced here is acceptable per se. The filesystem introduced is > being used to house the data generated by i915 driver in this patch series, > but will hopefully be generic enough to provide scope for usage by any > other drm subsystem component. > > The patch series is being floated as RFC to gather feedback on the idea and > infrastructure proposed here and it's suitability to address the specific > problem statement/use case. > > v2: fix the bat failures caused due to missing config check > > v3: Changes made: > - Move the location of drmfs from fs/ to drivers/gpu/drm/ (Chris) > - Moving config checks to header (Chris,Daniel) > > v4: Added the kernel Documentaion (using Sphinx). > > Sourab Gupta (4): > drm: Introduce drmfs pseudo filesystem interfaces > drm: Register drmfs filesystem from drm init > drm: Create driver specific root directory inside drmfs > drm/i915: Creating guc log file in drmfs instead of debugfs > > Documentation/gpu/drm-uapi.rst | 76 ++++ > drivers/gpu/drm/Kconfig | 9 + > drivers/gpu/drm/Makefile | 1 + > drivers/gpu/drm/drm_drv.c | 26 ++ > drivers/gpu/drm/drmfs.c | 566 ++++++++++++++++++++++++++ > drivers/gpu/drm/i915/i915_guc_submission.c | 33 +- > include/drm/drm_drv.h | 3 + > include/drm/drmfs.h | 77 ++++ > include/uapi/linux/magic.h | 3 + > 9 files changed, 773 insertions(+), 21 deletions(-) > create mode 100644 drivers/gpu/drm/drmfs.c > create mode 100644 include/drm/drmfs.h -- Regards, Laurent Pinchart _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
