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Date:   Thu, 4 Aug 2022 11:50:29 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Oded Gabbay <oded.gabbay@gmail.com>
Cc:     Dave Airlie <airlied@gmail.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Yuji Ishikawa <yuji2.ishikawa@toshiba.co.jp>,
        Jiho Chu <jiho.chu@samsung.com>, Arnd Bergmann <arnd@arndb.de>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>
Subject: Re: New subsystem for acceleration devices
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On Thu, Aug 04, 2022 at 10:43:42AM +0300, Oded Gabbay wrote:

> After all, memory management services, or common device chars handling
> I can get from other subsystems (e.g. rdma) as well. I'm sure I could
> model my uAPI to be rdma uAPI compliant (I can define proprietary uAPI
> there as well), but this doesn't mean I belong there, right ?

You sure can, but there is still an expectation, eg in RDMA, that your
device has a similarity to the established standards (like roce in
habana's case) that RDMA is geared to support.

I think the the most important thing to establish a new subsystem is
to actually identify what commonalities it is supposed to be
providing. Usually this is driven by some standards body, but the
AI/ML space hasn't gone in that direction at all yet.

We don't need a "subsystem" to have a bunch of drivers expose chardevs
with completely unique ioctls.

The flip is true of DRM - DRM is pretty general. I bet I could
implement an RDMA device under DRM - but that doesn't mean it should
be done.

My biggest concern is that this subsystem not turn into a back door
for a bunch of abuse of kernel APIs going forward. Though things are
better now, we still see this in DRM where expediency or performance
justifies hacky shortcuts instead of good in-kernel architecture. At
least DRM has reliable and experienced review these days.

Jason