Re: [RFC PATCH 0/3] new subsystem for compute accelerator devices

[Bagas Sanjaya]

On Sun, Oct 23, 2022 at 12:46:19AM +0300, Oded Gabbay wrote:
> In the last couple of months we had a discussion [1] about creating a new
> subsystem for compute accelerator devices in the kernel.
> 
> After an analysis that was done by DRM maintainers and myself, and following
> a BOF session at the Linux Plumbers conference a few weeks ago [2], we
> decided to create a new subsystem that will use the DRM subsystem's code and
> functionality. i.e. the accel core code will be part of the DRM subsystem.
> 
> This will allow us to leverage the extensive DRM code-base and
> collaborate with DRM developers that have experience with this type of
> devices. In addition, new features that will be added for the accelerator
> drivers can be of use to GPU drivers as well (e.g. RAS).
> 
> As agreed in the BOF session, the accelerator devices will be exposed to
> user-space with a new, dedicated device char files and a dedicated major
> number (261), to clearly separate them from graphic cards and the graphic
> user-space s/w stack. Furthermore, the drivers will be located in a separate
> place in the kernel tree (drivers/accel/).
> 
> This series of patches is the first step in this direction as it adds the
> necessary infrastructure for accelerator devices to DRM. The new devices will
> be exposed with the following convention:
> 
> device char files - /dev/accel/accel*
> sysfs             - /sys/class/accel/accel*/
> debugfs           - /sys/kernel/debug/accel/accel*/
> 
> I tried to reuse the existing DRM code as much as possible, while keeping it
> readable and maintainable.
> 
> One thing that is missing from this series is defining a namespace for the
> new accel subsystem, while I'll add in the next iteration of this patch-set,
> after I will receive feedback from the community.
> 
> As for drivers, once this series will be accepted (after adding the namespace),
> I will start working on migrating the habanalabs driver to the new accel
> subsystem. I have talked about it with Dave and we agreed that it will be
> a good start to simply move the driver as-is with minimal changes, and then
> start working on the driver's individual features that will be either added
> to the accel core code (with or without changes), or will be removed and
> instead the driver will use existing DRM code.
> 
> In addition, I know of at least 3 or 4 drivers that were submitted for review
> and are good candidates to be included in this new subsystem, instead of being
> a drm render node driver or a misc driver.
> 
> [1] https://lkml.org/lkml/2022/7/31/83
> [2] https://airlied.blogspot.com/2022/09/accelerators-bof-outcomes-summary.html
> 

Since this is new subsystem, it should have its own git tree where you
collected accelerator-related patches. By convention, there should be
"next" branch targeting for next kernel release and "fixes" branch for
bugfixes pending for current release. Both branches should be included
into linux-next. The names don't necessarily be that, though.

Also, it had been great if you write short, descriptive documentation
about the subsystem (maintainers handbook).

Cc'ing linux-doc folks.

-- 
An old man doll... just what I always wanted! - Clara

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