Re: [PATCH] remoteproc: qcom_q6v5: don't auto boot remote processor

From: Sibi Sankar
Date: Fri Jan 18 2019 - 23:17:56 EST

Hi Brian,
Thanks for the review

On 2019-01-19 02:34, Brian Norris wrote:
Hi Sibi,

On Fri, Jan 18, 2019 at 11:46 AM Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
On 2019-01-19 00:05, Brian Norris wrote:
> On Thu, Jan 17, 2019 at 11:04 PM Sibi Sankar <sibis@xxxxxxxxxxxxxx>
>> After experimenting with in kernel solutions for
>> three revisions and observing problems on graceful
>> shutdown usecase,
>
> What exactly were the problems again? e.g., what were the deficiencies
> with having the remoteproc device listen for the REMOTEFS_QMI_SVC_ID
> service again? Sorry, but I sort of dropped off on reviewing that
> stuff, and now I see this. I'd mildly prefer something that is
> actually automatic, but if I'm missing some aspects, I'd like to hear
> that. (And, I'd like to see them explained in the commit message, if
> this is ever to be merged.)

bringing down the modem after the RMTFS server
goes down leaves the modem in limbo (It has a few
pending rmtfs transactions that cannot go through)
which results in sysmon graceful shutdown failing.

Makes sense. Probably should be described in a re-send of this patch,
if we're going with that.

And we have to do a modem force-stop to proceed
which we want to avoid in graceful shutdown cases.

Shouldn't you do the "force-stop" in the kernel too? e.g., if rmtfs
daemon dies without doing a properly-timed stop, then we should still
force a stop in the kernel, no? Basically, why not do both mechanisms:
REMOTEFS_QMI_SVC-activated start/stop in the kernel, and manual stop
(and start? this likely might still be redundant) in the daemon?

yeah we already have that implemented in the kernel
i.e first we try graceful shutdown followed by
force-stop which will just timeout if graceful
shutdown was already completed. We would just call
stop from rmtfs without worrying about the underlying
details.


This is overcome by starting rproc mss from rmtfs
after REMOTEFS_QMI service is up and stopping
rproc mss from rmtfs on SIGKILL/SIGINT and other
program error signals before bringing down the
RMTFS_QMI service i.e before exiting the rmtfs
server loop.

That's still not really a sure-fire way of doing things. For one, you
can't catch SIGKILL. Similarly, you can't really clean up from OOM,
segfault, etc. So it would still be helpful to hook into the QMI
service notifications in the kernel, I think.

yes we would want a fail safe in the kernel
as well. Sorry I meant SIGTERM instead of
SIGKILL earlier


>> switching to controlling the
>> remoteproc mss through rmtfs seems to solve all
>> the known issues.
>
> How so? It explicitly does NOT help at all if RMTFS crashes.
> Because...who's going to stop the modem in that case? (It works if you
> automatically respawn a new RMTFS daemon, to toggle the modem. But
> that's kind of cheating, and you can do that anyway, even without this
> patch.) On the contrary, your patch *would* resolve that, since the
> modem would notice when the RMTFS server goes away, and it would stop
> itself.

yeah we would want to mimic what the kernel
patch did with the exception of stopping modem
before bringing down the rmtfs server (not toggle
rproc state but start on rmtfs service up and stop
before rmtfs server exit). So in that case we would
not want the modem to auto-boot.

See above. You can't really mimic what the kernel patch was doing
completely. You can try (which is probably a good idea), but you
should still have some fallback in the kernel, I expect.

yeah


>> https://patchwork.kernel.org/patch/10662395/
>>
>> we should probably get this merged in, now that
>> we are planning to start/stop mss through
>> rmtfs.
>
> Sorry, who's planning to stop mss through rmtfs? Did I miss something?

I have a working patch which I'll soon send
upstream for review, after it clears the internal
reviews/processes

OK.

Brian

--
-- Sibi Sankar --
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