linux-kernel - Re: [PATCH 1/3] remoteproc: Add Arm remoteproc driver

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Message-ID: <CANLsYkwOrtXxObL5MKf30OrUYB_uT=DnGEXUtfjH503r_LyMQA@mail.gmail.com>
Date: Tue, 26 Mar 2024 08:20:37 -0600
From: Mathieu Poirier <mathieu.poirier@...aro.org>
To: Abdellatif El Khlifi <abdellatif.elkhlifi@....com>
Cc: Sudeep Holla <sudeep.holla@....com>, Bjorn Andersson <andersson@...nel.org>, 
	Rob Herring <robh+dt@...nel.org>, Liviu Dudau <liviu.dudau@....com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Drew.Reed@....com, Adam.Johnston@....com, 
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH 1/3] remoteproc: Add Arm remoteproc driver

On Mon, 25 Mar 2024 at 11:13, Abdellatif El Khlifi
<abdellatif.elkhlifi@....com> wrote:
>
> Hi Mathieu,
>
> > > > > > > > > This is an initial patchset for allowing to turn on and off the remote processor.
> > > > > > > > > The FW is already loaded before the Corstone-1000 SoC is powered on and this
> > > > > > > > > is done through the FPGA board bootloader in case of the FPGA target. Or by the Corstone-1000 FVP model
> > > > > > > > > (emulator).
> > > > > > > > >
> > > > > > > > >From the above I take it that booting with a preloaded firmware is a
> > > > > > > > scenario that needs to be supported and not just a temporary stage.
> > > > > > >
> > > > > > > The current status of the Corstone-1000 SoC requires that there is
> > > > > > > a preloaded firmware for the external core. Preloading is done externally
> > > > > > > either through the FPGA bootloader or the emulator (FVP) before powering
> > > > > > > on the SoC.
> > > > > > >
> > > > > >
> > > > > > Ok
> > > > > >
> > > > > > > Corstone-1000 will be upgraded in a way that the A core running Linux is able
> > > > > > > to share memory with the remote core and also being able to access the remote
> > > > > > > core memory so Linux can copy the firmware to. This HW changes are still
> > > > > > > This is why this patchset is relying on a preloaded firmware. And it's the step 1
> > > > > > > of adding remoteproc support for Corstone.
> > > > > > >
> > > > > >
> > > > > > Ok, so there is a HW problem where A core and M core can't see each other's
> > > > > > memory, preventing the A core from copying the firmware image to the proper
> > > > > > location.
> > > > > >
> > > > > > When the HW is fixed, will there be a need to support scenarios where the
> > > > > > firmware image has been preloaded into memory?
> > > > >
> > > > > No, this scenario won't apply when we get the HW upgrade. No need for an
> > > > > external entity anymore. The firmware(s) will all be files in the linux filesystem.
> > > > >
> > > >
> > > > Very well.  I am willing to continue with this driver but it does so little that
> > > > I wonder if it wouldn't simply be better to move forward with upstreaming when
> > > > the HW is fixed.  The choice is yours.
> > > >
> > >
> > > I think Robin has raised few points that need clarification. I think it was
> > > done as part of DT binding patch. I share those concerns and I wanted to
> > > reaching to the same concerns by starting the questions I asked on corstone
> > > device tree changes.
> > >
> >
> > I also agree with Robin's point of view.  Proceeding with an initial
> > driver with minimal functionality doesn't preclude having complete
> > bindings.  But that said and as I pointed out, it might be better to
> > wait for the HW to be fixed before moving forward.
>
> We checked with the HW teams. The missing features will be implemented but
> this will take time.
>
> The foundation driver as it is right now is still valuable for people wanting to
> know how to power control Corstone external systems in a future proof manner
> (even in the incomplete state). We prefer to address all the review comments
> made so it can be merged. This includes making the DT binding as complete as
> possible as you advised. Then, once the HW is ready, I'll implement the comms
> and the FW reload part. Is that OK please ?
>

I'm in agreement with that plan as long as we agree the current
preloaded heuristic is temporary and is not a valid long term
scenario.

> Cheers,
> Abdellatif