linux-kernel - Re: [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF

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Date:   Mon, 21 Jun 2021 11:17:56 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Oded Gabbay <ogabbay@...nel.org>, Christoph Hellwig <hch@....de>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, Doug Ledford <dledford@...hat.com>,
        "airlied@...il.com" <airlied@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Tomer Tayar <ttayar@...ana.ai>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF

On Mon, Jun 21, 2021 at 02:28:48PM +0200, Daniel Vetter wrote:

> Mission acomplished, we've gone full circle, and the totally-not-a-gpu
> driver is now trying to use gpu infrastructure. And seems to have
> gained vram meanwhile too. Next up is going to be synchronization
> using dma_fence so you can pass buffers back&forth without stalls
> among drivers.

Well, we can't even see the other side of this so who knows

This is a new uAPI, where is the userspace? In RDMA at least I require
to see the new userspace and test suite before changes to
include/uapi/rdma can go ahead.

> Doug/Jason from infiniband: Should we add linux-rdma to the dma-buf
> wildcard match so that you can catch these next time around too? At
> least when people use scripts/get_maintainers.pl correctly. All the
> other subsystems using dma-buf are on there already (dri-devel,
> linux-media and linaro-mm-sig for android/arm embedded stuff).

My bigger concern is this doesn't seem to be implementing PCI P2P DMA
correctly. This is following the same hacky NULL page approach that
Christoph Hellwig already NAK'd for AMD.

This should not be allowed to proliferate.

I would be much happier seeing this be done using the approach of
Logan's series here:

https://lore.kernel.org/linux-block/20210513223203.5542-1-logang@deltatee.com/

Jason