[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <6f756dec-b386-a822-5f52-c121c00525b4@quicinc.com>
Date: Mon, 7 Nov 2022 09:07:28 -0700
From: Jeffrey Hugo <quic_jhugo@...cinc.com>
To: Oded Gabbay <ogabbay@...nel.org>, David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
<linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
Jason Gunthorpe <jgg@...dia.com>,
John Hubbard <jhubbard@...dia.com>,
Alex Deucher <alexander.deucher@....com>,
Matthew Wilcox <willy@...radead.org>
CC: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
Jiho Chu <jiho.chu@...sung.com>,
Daniel Stone <daniel@...ishbar.org>,
Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
Christoph Hellwig <hch@...radead.org>,
Kevin Hilman <khilman@...libre.com>,
Jagan Teki <jagan@...rulasolutions.com>,
Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>,
Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>,
Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [RFC PATCH v3 0/3] new subsystem for compute accelerator devices
On 11/6/2022 2:02 PM, Oded Gabbay wrote:
> This is the third version of the RFC following the comments given on the
> second version, but more importantly, following testing done by the VPU
> driver people and myself. We found out that there is a circular dependency
> between DRM and accel. DRM calls accel exported symbols during init and when
> accel devices are registering (all the minor handling), then accel calls DRM
> exported symbols. Therefore, if the two components are compiled as modules,
> there is a circular dependency.
>
> To overcome this, I have decided to compile the accel core code as part of
> the DRM kernel module (drm.ko). IMO, this is inline with the spirit of the
> design choice to have accel reuse the DRM core code and avoid code
> duplication.
>
> Another important change is that I have reverted back to use IDR for minor
> handling instead of xarray. This is because I have found that xarray doesn't
> handle well the scenario where you allocate a NULL entry and then exchange it
> with a real pointer. It appears xarray still considers that entry a "zero"
> entry. This is unfortunate because DRM works that way (first allocates a NULL
> entry and then replaces the entry with a real pointer).
>
> I decided to revert to IDR because I don't want to hold up these patches,
> as many people are blocked until the support for accel is merged. The xarray
> issue should be fixed as a separate patch by either fixing the xarray code or
> changing how DRM + ACCEL do minor id handling.
This sounds sane to me. However, this appears to be something that
Matthew Wilcox should be aware of (added for visibility). Perhaps he
has a very quick solution. If not, at-least he might have ideas on how
to best address in the future.
> The patches are in the following repo:
> https://git.kernel.org/pub/scm/linux/kernel/git/ogabbay/accel.git/log/?h=accel_v3
>
> As in v2, The HEAD of that branch is a commit adding a dummy driver that
> registers an accel device using the new framework. This can be served
> as a simple reference. I have checked inserting and removing the dummy driver,
> and opening and closing /dev/accel/accel0 and nothing got broken :)
>
> v1 cover letter:
> https://lkml.org/lkml/2022/10/22/544
>
> v2 cover letter:
> https://lore.kernel.org/lkml/20221102203405.1797491-1-ogabbay@kernel.org/T/
>
> Thanks,
> Oded.
>
> Oded Gabbay (3):
> drivers/accel: define kconfig and register a new major
> accel: add dedicated minor for accelerator devices
> drm: initialize accel framework
>
> Documentation/admin-guide/devices.txt | 5 +
> MAINTAINERS | 8 +
> drivers/Kconfig | 2 +
> drivers/accel/Kconfig | 24 ++
> drivers/accel/drm_accel.c | 322 ++++++++++++++++++++++++++
> drivers/gpu/drm/Makefile | 1 +
> drivers/gpu/drm/drm_drv.c | 102 +++++---
> drivers/gpu/drm/drm_file.c | 2 +-
> drivers/gpu/drm/drm_sysfs.c | 24 +-
> include/drm/drm_accel.h | 97 ++++++++
> include/drm/drm_device.h | 3 +
> include/drm/drm_drv.h | 8 +
> include/drm/drm_file.h | 21 +-
> 13 files changed, 582 insertions(+), 37 deletions(-)
> create mode 100644 drivers/accel/Kconfig
> create mode 100644 drivers/accel/drm_accel.c
> create mode 100644 include/drm/drm_accel.h
>
> --
> 2.25.1
>
Powered by blists - more mailing lists