linux-kernel - Re: remoteproc: Load coprocessor code to the specific main memory location

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Date:	Wed, 25 Jan 2012 15:45:48 +0200
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	monstr@...str.eu
Cc:	LKML <linux-kernel@...r.kernel.org>,
	John Williams <john.williams@...alogix.com>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	"Grosen, Mark" <mgrosen@...com>, Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: remoteproc: Load coprocessor code to the specific main memory location

On Wed, Jan 25, 2012 at 2:41 PM, Michal Simek <monstr@...str.eu> wrote:
> First of all will be the best to describe what we want to achieve.
> We have Zynq platform ARM Cortex-A9(which should be ARMv7 - 2cpus).
> cpu0 runs Linux and cpu1 will be used for real-time os. We would like to use
> remoteproc for loading any code(firmware if you like) for the cpu1 and start
> it.

Sounds cool.

So you're not < ARMv6, and I now understand why you bumped into that
code path: you're using a vanilla kernel, without CMA.

I suggest you merge Marek's CMA branch into your tree. Though 1MB
isn't that much really, and you can easily get away even without CMA.
You just won't have any non-CMA public example to use as a reference
;).

For details about the CMA tree and branches, see Marek's email:

https://lkml.org/lkml/2012/1/10/48

> Then in zynq_rproc_kick I copy content of this 1MB carveout to 0x0 physical

I recommend to keep the ->kick() handler as light as possible, as it
may be frequently triggered (think of a network driver doing I/O).

Ideally you should do the minimum required to only wake up the other
core when you are kicked. Copying a 1MB region every kick sounds
excessive.

> The main my problem is that firmware base addr must be at the beginning of
> address space
> or selected address but it is fixed and known.
..
> ok. How do you handle limitations if coprocessor expect code on any address?

Just make sure you reserve the CMA region at that fixed address.

For a reference how this can be done, look for OMAP_RPROC_CMA_BASE in
my rpmsg_3.2_rc4 branch.

>> Looping in Mark, who did the davinci remoteproc support, and might
>> have the code available to share. Hopefully we'd have the patches
>> posted soon, and then no-iommu platforms could just use them for
>> reference.
>
>
> ok. great. Will look forward for that code and recommendation because I am
> ARM newbie.

So I no longer think you need the davinci code, you can just follow
the OMAP example.

> I am also interested in suggestions about DTS binding. Have someone tried to
> describe it or use it?

No, AFAICT. And I'm not sure there are DTS binding for CMA regions
yet. Feel free to take a stab at it though ;)

Regards,
Ohad.
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