From: "Christian König" <ckoenig.leichtzumerken@gmail.com>
To: "Christoph Hellwig" <hch@infradead.org>,
"Jerome Glisse" <jglisse@redhat.com>,
"Christian König" <christian.koenig@amd.com>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Logan Gunthorpe" <logang@deltatee.com>,
"Dan Williams" <dan.j.williams@intel.com>
Subject: Re: [PATCH 4/8] dma-buf: add peer2peer flag
Date: Fri, 20 Apr 2018 10:58:50 +0200 [thread overview]
Message-ID: <3e17afc5-7d6c-5795-07bd-f23e34cf8d4b@gmail.com> (raw)
In-Reply-To: <20180420071312.GF31310@phenom.ffwll.local>
Am 20.04.2018 um 09:13 schrieb Daniel Vetter:
> On Thu, Apr 19, 2018 at 01:16:57AM -0700, Christoph Hellwig wrote:
>> On Mon, Apr 16, 2018 at 03:38:56PM +0200, Daniel Vetter wrote:
>>> We've broken that assumption in i915 years ago. Not struct page backed
>>> gpu memory is very real.
>>>
>>> Of course we'll never feed such a strange sg table to a driver which
>>> doesn't understand it, but allowing sg_page == NULL works perfectly
>>> fine. At least for gpu drivers.
>> For GPU drivers on x86 with no dma coherency problems, sure. But not
>> all the world is x86. We already have problems due to dmabugs use
>> of the awkward get_sgtable interface (see the common on
>> arm_dma_get_sgtable that I fully agree with), and doing this for memory
>> that doesn't have a struct page at all will make things even worse.
> x86 dma isn't coherent either, if you're a GPU :-) Flushing gpu caches
> tends to be too expensive, so there's pci-e support and chipset support to
> forgo it. Plus drivers flushing caches themselves.
>
> The dma_get_sgtable thing is indeed fun, right solution would probably be
> to push the dma-buf export down into the dma layer. The comment for
> arm_dma_get_sgtable is also not a realy concern, because dma-buf also
> abstracts away the flushing (or well is supposed to), so there really
> shouldn't be anyone calling the streaming apis on the returned sg table.
> That's why dma-buf gives you an sg table that's mapped already.
>
>>> If that's not acceptable then I guess we could go over the entire tree
>>> and frob all the gpu related code to switch over to a new struct
>>> sg_table_might_not_be_struct_page_backed, including all the other
>>> functions we added over the past few years to iterate over sg tables.
>>> But seems slightly silly, given that sg tables seem to do exactly what
>>> we need.
>> It isn't silly. We will have to do some surgery like that anyway
>> because the current APIs don't work. So relax, sit back and come up
>> with an API that solves the existing issues and serves us well in
>> the future.
> So we should just implement a copy of sg table for dma-buf, since I still
> think it does exactly what we need for gpus?
>
> Yes there's a bit a layering violation insofar that drivers really
> shouldn't each have their own copy of "how do I convert a piece of dma
> memory into dma-buf", but that doesn't render the interface a bad idea.
Completely agree on that.
What we need is an sg_alloc_table_from_resources(dev, resources,
num_resources) which does the handling common to all drivers.
Christian.
> -Daniel
next prev parent reply other threads:[~2018-04-20 8:58 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-25 10:59 [PATCH 1/8] lib/scatterlist: add sg_set_dma_addr() helper Christian König
2018-03-25 10:59 ` [PATCH 2/8] PCI: Add pci_find_common_upstream_dev() Christian König
2018-03-28 12:38 ` Christoph Hellwig
2018-03-28 15:07 ` Christian König
2018-03-28 15:47 ` Logan Gunthorpe
2018-03-28 16:02 ` Christian König
2018-03-28 16:25 ` Logan Gunthorpe
2018-03-28 18:28 ` Christian König
2018-03-28 18:57 ` Logan Gunthorpe
2018-03-28 19:44 ` Christian König
2018-03-28 19:53 ` Logan Gunthorpe
2018-03-29 11:44 ` Christian König
2018-03-29 15:45 ` Logan Gunthorpe
2018-03-29 16:10 ` Christian König
2018-03-29 16:25 ` Logan Gunthorpe
2018-03-29 18:15 ` Christian König
2018-03-30 1:58 ` Jerome Glisse
2018-03-30 6:33 ` Christoph Hellwig
2018-03-30 15:25 ` Jerome Glisse
2018-03-30 18:46 ` Logan Gunthorpe
2018-03-30 19:45 ` Jerome Glisse
2018-04-02 17:02 ` Logan Gunthorpe
2018-04-02 17:20 ` Jerome Glisse
2018-04-02 17:37 ` Logan Gunthorpe
2018-04-02 19:16 ` Jerome Glisse
2018-04-02 19:32 ` Logan Gunthorpe
2018-04-02 19:45 ` Jerome Glisse
[not found] ` <CADnq5_P-z=Noos_jaME9_CERri3C-m2hPPvx2bArr36O=1FnrA@mail.gmail.com>
2018-03-29 14:37 ` Alex Deucher
2018-03-25 10:59 ` [PATCH 3/8] PCI: Add pci_peer_traffic_supported() Christian König
2018-03-25 10:59 ` [PATCH 4/8] dma-buf: add peer2peer flag Christian König
2018-03-29 6:57 ` Daniel Vetter
2018-03-29 11:34 ` Christian König
2018-04-03 9:09 ` Daniel Vetter
2018-04-03 17:06 ` Jerome Glisse
2018-04-03 18:08 ` Daniel Vetter
2018-04-16 12:39 ` Christoph Hellwig
2018-04-16 13:38 ` Daniel Vetter
2018-04-19 8:16 ` Christoph Hellwig
2018-04-20 7:13 ` Daniel Vetter
2018-04-20 8:58 ` Christian König [this message]
2018-04-20 10:17 ` Christoph Hellwig
2018-04-20 10:44 ` Christian König
2018-04-20 12:46 ` Christoph Hellwig
2018-04-20 15:21 ` [Linaro-mm-sig] " Daniel Vetter
2018-04-24 18:48 ` Christoph Hellwig
2018-04-24 19:32 ` Daniel Vetter
2018-04-25 5:48 ` Christoph Hellwig
2018-04-25 6:10 ` Alex Deucher
2018-04-25 6:13 ` Daniel Vetter
2018-04-25 6:23 ` Daniel Vetter
2018-04-25 6:43 ` Christoph Hellwig
2018-04-25 7:02 ` Daniel Vetter
2018-04-25 7:09 ` Christoph Hellwig
2018-04-25 7:30 ` Daniel Vetter
2018-04-25 7:56 ` Thierry Reding
2018-04-25 8:55 ` Christoph Hellwig
2018-04-25 7:43 ` Thierry Reding
2018-04-25 7:41 ` Thierry Reding
2018-04-25 8:54 ` noveau vs arm dma ops Christoph Hellwig
2018-04-25 9:25 ` Russell King - ARM Linux
2018-04-25 10:04 ` Daniel Vetter
2018-04-25 15:33 ` Christoph Hellwig
2018-04-25 21:35 ` Daniel Vetter
2018-04-25 23:26 ` Russell King - ARM Linux
2018-04-26 9:17 ` Daniel Vetter
2018-04-26 9:09 ` Christoph Hellwig
2018-04-26 9:45 ` Daniel Vetter
2018-04-26 11:12 ` Russell King - ARM Linux
2018-04-25 22:54 ` Russell King - ARM Linux
2018-04-26 9:13 ` Christoph Hellwig
2018-04-26 9:20 ` [Linaro-mm-sig] " Daniel Vetter
2018-04-26 9:24 ` Christoph Hellwig
2018-04-26 9:39 ` Daniel Vetter
2018-04-25 6:24 ` [Linaro-mm-sig] [PATCH 4/8] dma-buf: add peer2peer flag Alex Deucher
2018-04-25 6:41 ` Christoph Hellwig
2018-04-25 17:44 ` Alex Deucher
2018-04-25 18:38 ` Dan Williams
2018-05-04 12:45 ` Lucas Stach
2018-03-25 10:59 ` [PATCH 5/8] drm/amdgpu: print DMA-buf status in debugfs Christian König
2018-03-25 10:59 ` [PATCH 6/8] drm/amdgpu: note that we can handle peer2peer DMA-buf Christian König
2018-03-25 10:59 ` [PATCH 7/8] drm/amdgpu: add amdgpu_gem_attach Christian König
2018-03-25 11:00 ` [PATCH 8/8] drm/amdgpu: add support for exporting VRAM using DMA-buf Christian König
2018-03-28 12:37 ` [PATCH 1/8] lib/scatterlist: add sg_set_dma_addr() helper Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3e17afc5-7d6c-5795-07bd-f23e34cf8d4b@gmail.com \
--to=ckoenig.leichtzumerken@gmail.com \
--cc=amd-gfx@lists.freedesktop.org \
--cc=christian.koenig@amd.com \
--cc=dan.j.williams@intel.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=hch@infradead.org \
--cc=jglisse@redhat.com \
--cc=linaro-mm-sig@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-media@vger.kernel.org \
--cc=logang@deltatee.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).