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Message-ID: <899fe0ce-b6d7-c138-04b6-4b12405f8d93@amd.com>
Date: Thu, 24 Jun 2021 11:52:47 +0200
From: Christian König <christian.koenig@....com>
To: Christoph Hellwig <hch@....de>
Cc: Oded Gabbay <oded.gabbay@...il.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Christian König <ckoenig.leichtzumerken@...il.com>,
Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
linux-rdma <linux-rdma@...r.kernel.org>,
Oded Gabbay <ogabbay@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@...ts.linaro.org>,
Doug Ledford <dledford@...hat.com>,
Tomer Tayar <ttayar@...ana.ai>,
amd-gfx list <amd-gfx@...ts.freedesktop.org>,
Greg KH <gregkh@...uxfoundation.org>,
Alex Deucher <alexander.deucher@....com>,
Leon Romanovsky <leonro@...dia.com>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export
FD for DMA-BUF
Am 24.06.21 um 10:12 schrieb Christoph Hellwig:
> On Thu, Jun 24, 2021 at 10:07:14AM +0200, Christian König wrote:
>> The key point is that accessing the underlying pages even when DMA-bufs are
>> backed by system memory is illegal. Daniel even created a patch which
>> mangles the page pointers in sg_tables used by DMA-buf to make sure that
>> people don't try to use them.
> Which is another goddamn layering violation of a subsystem that has no
> business at all poking into the scatterlist structure, yes.
Completely agree, but it is also the easiest way to get away from the
scatterlist as trasnport vehicle for the dma_addresses.
[SNIP]
>> My best plan to get out of this mess is that we change the DMA-buf
>> interface to use an array of dma_addresses instead of the sg_table object
>> and I have already been working on this actively the last few month.
> Awesome! I have a bit of related work on the DMA mapping subsystems, so
> let's sync up as soon as you have some first sketches.
Don't start cheering to fast.
I've already converted a bunch of the GPU drivers, but there are at
least 6 GPU still needing to be fixed and on top of that comes VA-API
and a few others.
What are your plans for the DMA mapping subsystem?
> Btw, one thing I noticed when looking over the dma-buf instances is that
> there is a lot of duplicated code for creating a sg_table from pages,
> and then mapping it. It would be good if we could move toward common
> helpers instead of duplicating that all over again.
Can you give an example?
Thanks,
Christian.
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