Re: [PATCH v2 0/4] drm/nvdla: Add driver support for NVDLA

[Thierry Reding <thierry.reding@gmail.com>]

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On Fri, Apr 29, 2022 at 11:28:10AM +0800, Cai Huoqing wrote:
> On 28 4月 22 18:56:07, Mikko Perttunen wrote:
> > On 4/28/22 17:10, Thierry Reding wrote:
> > > On Tue, Apr 26, 2022 at 02:07:57PM +0800, Cai Huoqing wrote:
> > > > The NVIDIA Deep Learning Accelerator (NVDLA) is an open source IP
> > > > which is integrated into NVIDIA Jetson AGX Xavier,
> > > > so add driver support for this accelerator."
> > > 
> > > Hi,
> > > 
> > > nice to see this work going on. For subsequent revisions, can you please
> > > also Cc the Tegra mailing list (linux-tegra@vger.kernel.org) as well as
> > > the Tegra platform maintainers (that's Jon Hunter and myself). This will
> > > make sure that more people with an interest in this will see your work.
> > > Not everyone follows dri-devel, linaro-mm-sig or linux-media.
> > > 
> > > Thanks,
> > > Thierry
> > 
> > From a quick glance it looks like this driver pokes DLA hardware directly
> > which is not the intended programming model on Tegra hardware (there are
> > Falcon microcontrollers that offload task scheduling and synchronization
> > from the CPU). The hardware is also behind the Host1x bus so a simple
> > platform device is not sufficient.
> > 
> > Was this driver developed against some platform with OpenDLA hardware (i.e.
> > not Tegra)?
> > 
> > If so, we'd need to verify if the hardware matches the hardware in Tegra194.
> > Also, this driver may not be ideal for Tegra platforms since we would lack
> > the hardware scheduling and synchronization facilities. It is likely
> > necessary to have separate drivers for OpenDLA and Tegra's DLA integration.
> > 
> > Thanks,
> > Mikko
> > 
> Tegra DLA seems to work with a slave coprocessor, the host driver just
> impelement message queue, share buffer, notification... The hardware
> detail of DLA maybe in the slave driver(not linux OS?).
> 
> Sure, This driver just support for the SOCs or FPGAs that OPENDLA
> inside. I will change this kind of description "integrated into NVIDIA Jetson AGX Xavier"
> this driver dont support for Tegra directly.

Yes, I think it would be good to make it clear that this is not going to
work with the Tegra instantiations so that people don't get confused.

I think it would be ideal, though, if we could reuse as much of this
driver as possible to work with other instantiations. The only reference
to OpenDLA that I can find and which seems somehow relevant to this is
here:

	https://github.com/SCLUO/ITRI-OpenDLA

Is that the version that you're using? Or is the version that you're
using at least compatible with that one? Apart from that and the Tegra
instantiations, are you aware of any other derivatives that we need to
account for? I'm worried that this might fragment to the point where it
becomes unmaintainable in upstream Linux.

Even if this doesn't concern the Tegra instantiation, I think most of my
other comments remain valid. Things like global variables will get in
the way of multiple FPGA instantiations as well, for example.

You will also need to provide the device tree bindings for the
particular instantiation that you're working on. Typically this would be
identified by a vendor-specific compatible string for your particular
board, but if it stems from a "canonical" FPGA mapping, matching on that
compatible string might also be an option. In either case, when you send
out the DT bindings, please include the devicetree@vger.kernel.org
mailing list so that they can be properly reviewed.

Thierry

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