From: Minchan Kim <minchan@kernel.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Hyesoo Yu <hyesoo.yu@samsung.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Matthew Wilcox <willy@infradead.org>,
david@redhat.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz,
Suren Baghdasaryan <surenb@google.com>,
KyongHo Cho <pullip.cho@samsung.com>,
John Dias <joaodias@google.com>,
Hridya Valsaraju <hridya@google.com>,
Sumit Semwal <sumit.semwal@linaro.org>,
Brian Starkey <Brian.Starkey@arm.com>,
linux-media <linux-media@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>, Rob Herring <robh@kernel.org>,
Christian Koenig <christian.koenig@amd.com>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>
Subject: Re: [PATCH 4/4] dma-heap: Devicetree binding for chunk heap
Date: Wed, 9 Dec 2020 15:53:27 -0800 [thread overview]
Message-ID: <X9Fjd+eSStUJskOV@google.com> (raw)
In-Reply-To: <CALAqxLV=r-V6u8hq2fTmxq855nT7QPkkjyAYdPeZRkYPBi_CKg@mail.gmail.com>
On Wed, Nov 18, 2020 at 07:19:07PM -0800, John Stultz wrote:
> On Wed, Nov 18, 2020 at 5:22 PM Hyesoo Yu <hyesoo.yu@samsung.com> wrote:
> >
> > On Tue, Nov 17, 2020 at 07:00:54PM -0800, John Stultz wrote:
> > > So I suspect Rob will push back on this as he has for other dt
> > > bindings related to ion/dmabuf heaps (I tried to push a similar
> > > solution to exporting multiple CMA areas via dmabuf heaps).
> > >
> > > The proposal he seemed to like best was having an in-kernel function
> > > that a driver would call to initialize the heap (associated with the
> > > CMA region the driver is interested in). Similar to Kunihiko Hayashi's
> > > patch here:
> > > - https://lore.kernel.org/lkml/1594948208-4739-1-git-send-email-hayashi.kunihiko@socionext.com/
> > >
> > > The one sticking point for that patch (which I think is a good one),
> > > is that we don't have any in-tree users, so it couldn't be merged yet.
> > >
> > > A similar approach might be good here, but again we probably need to
> > > have at least one in-tree user which could call such a registration
> > > function.
> >
> > Thanks for your review.
> >
> > The chunk heap is not considered for device-specific reserved memory and specific driver.
> > It is similar to system heap, but it only collects high-order pages by using specific cma-area for performance.
>
> So, yes I agree, the chunk heap isn't device specific. It's just that
> the CMA regions usually are tied to devices.
>
> The main objection to this style of solution has been due to the fact
> that the DTS is supposed to describe the physical hardware (in an OS
> agnostic way), rather than define configuration info for Linux
> software drivers.
>
> Obviously this can be quibbled about, as the normal way of tying
> devices to CMA has some assumptions of what the driver will use that
> region for, rather than somehow representing a physical tie between a
> memory reservation and a device. Nonetheless, Rob has been hesitant to
> take any sort of ION/DmaBuf Heap DT devices, and has been more
> interested in some device having the memory reservation reference and
> the driver for that doing the registration.
>
> > It is strange that there is in-tree user who registers chunk heap.
> > (Wouldn't it be strange for some users to register the system heap?)
>
> Well, as there's no reservation/configuration needed, the system heap
> can register itself.
>
> The CMA heap currently only registers the default CMA heap, as we
> didn't want to expose all CMA regions and there's otherwise no way to
> pick and choose.
Yub.
dma-buf really need a way to make exclusive CMA area. Otherwise, default
CMA would be shared among drivers and introduce fragmentation easily
since we couldn't control other drivers. In such aspect, I don't think
current cma-heap works if userspace needs big memory chunk.
Here, the problem is there is no in-kernel user to bind the specific
CMA area because the owner will be random in userspace via dma-buf
interface.
>
> > Is there a reason to use dma-heap framework to add cma-area for specific device ?
> >
> > Even if some in-tree users register dma-heap with cma-area, the buffers could be allocated in user-land and these could be shared among other devices.
> > For exclusive access, I guess, the device don't need to register dma-heap for cma area.
> >
>
> It's not really about exclusive access. More just that if you want to
> bind a memory reservation/region (cma or otherwise), at least for DTS,
> it needs to bind with some device in DT.
>
> Then the device driver can register that region with a heap driver.
> This avoids adding new Linux-specific software bindings to DT. It
> becomes a driver implementation detail instead. The primary user of
> the heap type would probably be a practical pick (ie the display or
> isp driver).
If it's the only solution, we could create some dummy driver which has
only module_init and bind it from there but I don't think it's a good
idea.
>
> The other potential solution Rob has suggested is that we create some
> tag for the memory reservation (ie: like we do with cma: "reusable"),
> which can be used to register the region to a heap. But this has the
> problem that each tag has to be well defined and map to a known heap.
Do you think that's the only solution to make progress for this feature?
Then, could you elaborate it a bit more or any other ideas from dma-buf
folks?
next prev parent reply other threads:[~2020-12-09 23:53 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 18:19 [PATCH 0/4] Chunk Heap Support on DMA-HEAP Minchan Kim
2020-11-17 18:19 ` [PATCH 1/4] mm: introduce cma_alloc_bulk API Minchan Kim
2020-11-23 14:15 ` David Hildenbrand
2020-11-25 20:12 ` Minchan Kim
2020-11-17 18:19 ` [PATCH 2/4] dma-buf: add export symbol for dma-heap Minchan Kim
2020-11-18 5:18 ` John Stultz
2020-11-17 18:19 ` [PATCH 3/4] dma-buf: heaps: add chunk heap to dmabuf heaps Minchan Kim
2020-11-18 9:00 ` Hillf Danton
2020-11-19 1:16 ` Hyesoo Yu
2020-11-17 18:19 ` [PATCH 4/4] dma-heap: Devicetree binding for chunk heap Minchan Kim
2020-11-18 3:00 ` John Stultz
2020-11-19 1:14 ` Hyesoo Yu
2020-11-19 3:19 ` John Stultz
2020-11-19 6:30 ` Hyesoo Yu
2020-12-09 23:53 ` Minchan Kim [this message]
2020-12-10 8:15 ` John Stultz
2020-12-10 16:06 ` Minchan Kim
2020-12-10 22:40 ` John Stultz
2020-12-10 23:30 ` Minchan Kim
2020-12-08 16:56 ` [PATCH 0/4] Chunk Heap Support on DMA-HEAP Nicolas Dufresne
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=X9Fjd+eSStUJskOV@google.com \
--to=minchan@kernel.org \
--cc=Brian.Starkey@arm.com \
--cc=akpm@linux-foundation.org \
--cc=christian.koenig@amd.com \
--cc=david@redhat.com \
--cc=devicetree@vger.kernel.org \
--cc=hridya@google.com \
--cc=hyesoo.yu@samsung.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=joaodias@google.com \
--cc=john.stultz@linaro.org \
--cc=linaro-mm-sig@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-media@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=pullip.cho@samsung.com \
--cc=robh@kernel.org \
--cc=sumit.semwal@linaro.org \
--cc=surenb@google.com \
--cc=vbabka@suse.cz \
--cc=willy@infradead.org \
/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).