linux-kernel - Re: [PATCH v4 0/2] Add p2p via dmabuf to habanalabs

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Date:   Tue, 6 Jul 2021 11:23:57 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Oded Gabbay <oded.gabbay@...il.com>,
        Oded Gabbay <ogabbay@...nel.org>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Doug Ledford <dledford@...hat.com>,
        Dave Airlie <airlied@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        Christoph Hellwig <hch@....de>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v4 0/2] Add p2p via dmabuf to habanalabs

On Tue, Jul 06, 2021 at 12:36:51PM +0200, Daniel Vetter wrote:

> If that means AI companies don't want to open our their hw specs
> enough to allow that, so be it - all you get in that case is
> offloading the kernel side  of the stack for convenience, with zero
> long term prospects to ever make this into a cross vendor subsystem
> stack that does something useful.

I don't think this is true at all - nouveau is probably the best
example.

nouveau reverse engineered a userspace stack for one of these devices.

How much further ahead would they have been by now if they had a
vendor supported, fully featured, open kernel driver to build the
userspace upon?

> open up your hw enough for that, I really don't see the point in
> merging such a driver, it'll be an unmaintainable stack by anyone else
> who's not having access to those NDA covered specs and patents and
> everything.

My perspective from RDMA is that the drivers are black boxes. I can
hack around the interface layers but there is a lot of wild stuff in
there that can't be understood without access to the HW documentation.

I think only HW that has open specs, like say NVMe, can really be
properly community oriented. Otherwise we have to work in a community
partnership with the vendor.

Jason