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

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Date:   Tue, 6 Jul 2021 18:07:17 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Jason Gunthorpe <jgg@...pe.ca>
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 6, 2021 at 5:49 PM Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> On Tue, Jul 6, 2021 at 5:25 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
> > I'm not sure about this all or nothing approach. AFAIK DRM has the
> > worst problems with out of tree drivers right now.
>
> Well I guess someone could stand up a drivers/totally-not-gpu and just
> let the flood in. Even duplicated drivers and everything included,
> because the vendor drivers are better. Worth a shot, we've practically
> started this already, I'm just not going to help with the cleanup.

tbh I think at this point someone should just do that. Ideally with
some boundary like please don't use dma-fence or dma-buf and stuff
like that so drivers/gpu doesn't ever have to deal with the fallout.
But way too many people think that somehow you magically get the other
90% of an open accel stack if you're just friendly enough and merge
the kernel driver, so we really should just that experiment in
upstream and watch it pan out in reality.

Minimally it would be some great entertainment :-)

Also on your claim that drivers/gpu is a non-upstream disaster: I've
also learned that that for drivers/rdma there's the upstream driver,
and then there's the out-of-tree hackjob the vendor actually supports.
So seems to be about the same level of screwed up, if you ask the
vendor they tell you the upstream driver isn't a thing they care about
and it's just done for a bit of goodwill. Except if you have enormous
amounts of volume, then suddenly it's an option ... Minus the fw issue
for nvidia, upstream does support all the gpus you can buy right now
and that can run on linux with some vendor driver (aka excluding apple
M1 and ofc upcoming products from most vendors).

drivers/accel otoh is mostly out-of-tree, because aside from Greg
mergin habanalabs no one is bold enough anymore to just merge them
all. There's lots of those going around that would be ready for
picking. And they've been continously submitted to upstream over the
years, even before the entire habanalabs thing.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch