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Date: Wed, 13 Mar 2024 10:25:32 -0600
From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Cc: Bjorn Andersson <andersson@kernel.org>,
	Rob Herring <robh+dt@kernel.org>, Liviu Dudau <liviu.dudau@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>, Drew.Reed@arm.com,
	Adam.Johnston@arm.com, linux-arm-kernel@lists.infradead.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-remoteproc@vger.kernel.org
Subject: Re: [PATCH 1/3] remoteproc: Add Arm remoteproc driver
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On Tue, Mar 12, 2024 at 05:32:52PM +0000, Abdellatif El Khlifi wrote:
> Hi Mathieu,
> 
> On Tue, Mar 12, 2024 at 10:29:52AM -0600, Mathieu Poirier wrote:
> > > 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?

> When the HW is ready, we will be able to avoid preloading the firmware
> and the user can do the following:
> 
> 1) Use a default firmware filename stated in the DT (firmware-name property),
> that's the one remoteproc subsystem will use initially, load the firmware file
> and start the remote core.
> 
> 2) Then, the user can choose to use another firmware file:
> 
>     echo stop >/sys/class/remoteproc/remoteproc0/state
>     echo -n new_firmware.elf > /sys/class/remoteproc/remoteproc0/firmware
>     echo start >/sys/class/remoteproc/remoteproc0/state
> 
> > > The plan for the driver is as follows:
> > >
> > > Step 1: provide a foundation driver capable of turning the core on/off
> > >
> > > Step 2: provide mailbox support for comms
> > >
> > > Step 3: provide FW reload capability
> > >
> > What happens when a user wants to boot the remote processor with the
> > firmware provided on the file system rather than the one preloaded
> > into memory?
> 
> We will support this scenario when the HW is upgraded and copying the firmware
> to the remote core memory becomes possible.
> 
> > Furthermore, how do we account for scenarios where the
> > remote processor goes from running a firmware image on the file system
> > to the firmware image loaded by an external entity?  Is this a valid
> > scenario?
> 
> 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.
> 
> > > Steps 2 & 3 are waiting for a HW update so the Cortex-A35 (running Linux) can share memory with
> > > the remote core.
> > >
> > > I'm happy to provide more explanation in the commit log to reflect this status.
> > >
> > > Is it OK that we go with step 1 as a foundation please ?
> > >
> > 
> > First let's clarify all the scenarios that need to be supported.  From
> > there I will advise on how to proceed and what modifications to the
> > subsystem's core should be made, if need be.
> 
> Thanks, I hope the answers above provide the information needed.
> 
> Cheers
> Abdellatif