linux-kernel - Re: [PATCH v5 8/8] rpmsg: Turn name service into a stand alone driver

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Date:   Mon, 9 Nov 2020 09:48:37 +0100
From:   Arnaud POULIQUEN <arnaud.pouliquen@...com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>
CC:     "ohad@...ery.com" <ohad@...ery.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 8/8] rpmsg: Turn name service into a stand alone driver

Hi Guennadi, Mathieu,

On 11/6/20 6:53 PM, Mathieu Poirier wrote:
> On Fri, Nov 06, 2020 at 03:00:28PM +0100, Guennadi Liakhovetski wrote:
>> On Fri, Nov 06, 2020 at 02:15:45PM +0100, Guennadi Liakhovetski wrote:
>>> Hi Mathieu, Arnaud,
>>>
>>> On Thu, Nov 05, 2020 at 03:50:28PM -0700, Mathieu Poirier wrote:
>>>> From: Arnaud Pouliquen <arnaud.pouliquen@...com>
>>>>
>>>> Make the RPMSG name service announcement a stand alone driver so that it
>>>> can be reused by other subsystems.  It is also the first step in making the
>>>> functionatlity transport independent, i.e that is not tied to virtIO.
>>>
>>> Sorry, I just realised that my testing was incomplete. I haven't tested 
>>> automatic module loading and indeed it doesn't work. If rpmsg_ns is loaded 
>>> it probes and it's working, but if it isn't loaded and instead the rpmsg 
>>> bus driver is probed (e.g. virtio_rpmsg_bus), calling 
>>> rpmsg_ns_register_device() to create a new rpmsg_ns device doesn't cause 
>>> rpmsg_ns to be loaded.
>>
>> A simple fix for that is using MODULE_ALIAS("rpmsg:rpmsg_ns"); in rpmsg_ns.c 
>> but that alone doesn't fix the problem completely - the module does load then 
>> but not quickly enough, the NS announcement from the host / remote arrives 
>> before rpmsg_ns has properly registered. I think the best solution would be 
>> to link rpmsg_ns.c together with rpmsg_core.c. You'll probably want to keep 
>> the module name, so you could rename them to just core.c and ns.c.
> 
> I'm pretty sure it is because virtio_device_ready() in rpmsg_probe() is called
> before the kernel has finished loading the name space driver.  There has to be
> a way to prevent that from happening - I will investigate further.

Right, no dependency is set so the rpmsg_ns driver is never probed...
And  name service announcement messages are dropped if the service is not present.

if rpmsg_virtio_bus is built-in
-> using "select RPMSG_NS" in RPMSG_VIRTIO kconfig should ensure that rpmsg_ns is also built-in 
if rpmsg_virtio_bus is build as module rpmsg_ns.ko should be loaded first.
-> MODULE_SOFTDEP could be used in virtio_rpmsg_bus.c

Thanks,
Arnaud

> 
> Thanks for reporting this,
> Mathieu
> 
>>
>> Thanks
>> Guennadi