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

Arnaud POULIQUEN
2020-11-09T08:49:01Z

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@st.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