Re: [RFC PATCH 0/4] Add a RPMsg driver to support AI Processing Unit (APU)

From: Daniel Vetter <daniel@ffwll.ch>
To: Alexandre Bailon <abailon@baylibre.com>
Cc: linux-remoteproc@vger.kernel.org, ohad@wizery.com,
	gpain@baylibre.com, stephane.leprovost@mediatek.com,
	jstephan@baylibre.com, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	mturquette@baylibre.com, bjorn.andersson@linaro.org,
	christian.koenig@amd.com, linux-media@vger.kernel.org
Subject: Re: [RFC PATCH 0/4] Add a RPMsg driver to support AI Processing Unit (APU)
Date: Fri, 2 Oct 2020 11:35:08 +0200	[thread overview]
Message-ID: <20201002093508.GF438822@phenom.ffwll.local> (raw)
In-Reply-To: <8e4bb739-c3b3-d790-e8e3-dd5df2d6f869@baylibre.com>

On Thu, Oct 01, 2020 at 07:28:27PM +0200, Alexandre Bailon wrote:
> Hi Daniel,
> 
> On 10/1/20 10:48 AM, Daniel Vetter wrote:
> > On Wed, Sep 30, 2020 at 01:53:46PM +0200, Alexandre Bailon wrote:
> > > This adds a RPMsg driver that implements communication between the CPU and an
> > > APU.
> > > This uses VirtIO buffer to exchange messages but for sharing data, this uses
> > > a dmabuf, mapped to be shared between CPU (userspace) and APU.
> > > The driver is relatively generic, and should work with any SoC implementing
> > > hardware accelerator for AI if they use support remoteproc and VirtIO.
> > > 
> > > For the people interested by the firmware or userspace library,
> > > the sources are available here:
> > > https://github.com/BayLibre/open-amp/tree/v2020.01-mtk/apps/examples/apu
> > Since this has open userspace (from a very cursory look), and smells very
> > much like an acceleration driver, and seems to use dma-buf for memory
> > management: Why is this not just a drm driver?
> 
> I have never though to DRM since for me it was only a RPMsg driver.
> I don't know well DRM. Could you tell me how you would do it so I could have
> a look ?

Well internally it would still be an rpmsg driver ... I'm assuming that's
kinda similar to how most gpu drivers sit on top of a pci_device or a
platform_device, it's just a means to get at your "device"?

The part I'm talking about here is the userspace api. You're creating an
entirely new chardev interface, which at least from a quick look seems to
be based on dma-buf buffers and used to submit commands to your device to
do some kind of computing/processing. That's exactly what drivers/gpu/drm
does (if you ignore the display/modeset side of things) - at the kernel
level gpus have nothing to do with graphics, but all with handling buffer
objects and throwing workloads at some kind of accelerator thing.

Of course that's just my guess of what's going on, after scrolling through
your driver and userspace a bit, I might be completely off. But if my
guess is roughly right, then your driver is internally an rpmsg
driver, but towards userspace it should be a drm driver.

Cheers, Daniel

> 
> Thanks,
> Alexandre
> 
> > -Daniel
> > 
> > > Alexandre Bailon (3):
> > >    Add a RPMSG driver for the APU in the mt8183
> > >    rpmsg: apu_rpmsg: update the way to store IOMMU mapping
> > >    rpmsg: apu_rpmsg: Add an IOCTL to request IOMMU mapping
> > > 
> > > Julien STEPHAN (1):
> > >    rpmsg: apu_rpmsg: Add support for async apu request
> > > 
> > >   drivers/rpmsg/Kconfig          |   9 +
> > >   drivers/rpmsg/Makefile         |   1 +
> > >   drivers/rpmsg/apu_rpmsg.c      | 752 +++++++++++++++++++++++++++++++++
> > >   drivers/rpmsg/apu_rpmsg.h      |  52 +++
> > >   include/uapi/linux/apu_rpmsg.h |  47 +++
> > >   5 files changed, 861 insertions(+)
> > >   create mode 100644 drivers/rpmsg/apu_rpmsg.c
> > >   create mode 100644 drivers/rpmsg/apu_rpmsg.h
> > >   create mode 100644 include/uapi/linux/apu_rpmsg.h
> > > 
> > > -- 
> > > 2.26.2
> > > 
> > > _______________________________________________
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> > > dri-devel@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch