remoteproc: imx_rproc race

[Peng Fan]

> Subject: remoteproc: imx_rproc race
> 
> Hi all,
> 
> to support remote processors started before Linux booted on i.MX8MP SoCs,
> the rsc-table device tree property was introduced.
> This entry specifies a location in a shared memory area where the remote
> processor will place the resource table.
> In the MCUXpresso SDK samples for i.MX8MP, this is achieved by copying the
> resource table to this location during startup.
> While this use case works fine, I don't see how this is supposed to work when
> booting the same remote processor firmware from user space.
> 
> Note that I expected "[PATCH V2] remoteproc: imx_rproc: use imx specific
> hook for find_loaded_rsc_table" [1] to be applied at some point.
> Without this patch there seem to be some other issues as well.
> 
> After starting the remote processor here:
> remoteproc_core.c: rproc_start(): 'ret = rproc->ops->start(rproc);'
> both cores are running in parallel and both cores are trying to write to the
> resource table.
> While Linux starts setting status flags like VIRTIO_CONFIG_S_DRIVER, the
> remote processor copies the entire resource table to the same place during
> its startup sequence.
> If the copy runs after Linux has set the status flags, those flags will be reset
> and the remote processor will wait for them forever. Since this is racy, this will
> most likely fail.

Technically your concern is valid, but NXP ATF has locked down TCM area,
that means linux has no chance to write TCM area for elf resource table update.

So I moved to use rsc_table.

NXP MCU SDK not check resource table per my understanding. It just copy the
resource table to the place rsc_table points to.

Regards,
Peng.

> 
> Can anyone tell me how it is intended to cover both cases (other than using
> different firmware images for the remote processor)?
> 
> Thanks
>   ~Matthias
> 
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