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From:   Mathieu Poirier <mathieu.poirier@linaro.org>
Date:   Wed, 8 Apr 2020 09:59:57 -0600
Message-ID: <CANLsYkxWSQNA0SqP5p1d_EK6am5rV-ONrvou1UyuNMnMjGW71Q@mail.gmail.com>
Subject: Re: [PATCH v2] rpmsg: core: Add wildcard match for name service
To:     Suman Anna <s-anna@ti.com>
Cc:     Arnaud POULIQUEN <arnaud.pouliquen@st.com>,
        Ohad Ben-Cohen <ohad@wizery.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-remoteproc <linux-remoteproc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, 7 Apr 2020 at 17:07, Suman Anna <s-anna@ti.com> wrote:
>
> Hi Mathieu, Arnaud,
>
> On 3/27/20 2:36 PM, Mathieu Poirier wrote:
> > On Fri, Mar 27, 2020 at 10:35:34AM +0100, Arnaud POULIQUEN wrote:
> >> Hi
> >>
> >> On 3/26/20 11:01 PM, Mathieu Poirier wrote:
> >>> On Thu, 26 Mar 2020 at 14:42, Suman Anna <s-anna@ti.com> wrote:
> >>>>
> >>>> On 3/26/20 3:21 PM, Mathieu Poirier wrote:
> >>>>> On Thu, 26 Mar 2020 at 09:06, Suman Anna <s-anna@ti.com> wrote:
> >>>>>>
> >>>>>> Hi Mathieu,
> >>>>>>
> >>>>>> On 3/10/20 10:50 AM, Mathieu Poirier wrote:
> >>>>>>> Adding the capability to supplement the base definition published
> >>>>>>> by an rpmsg_driver with a postfix description so that it is possible
> >>>>>>> for several entity to use the same service.
> >>>>>>>
> >>>>>>> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> >>>>>>> Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
> >>>>>>
> >>>>>> So, the concern I have here is that we are retrofitting this into the
> >>>>>> existing 32-byte name field, and the question is if it is going to be
> >>>>>> enough in general. That's the reason I went with the additional 32-byte
> >>>>>> field with the "rpmsg: add a description field" patch.
> >>>>>>
> >>>>>
> >>>>> That's a valid concern.
> >>>>>
> >>>>> Did you consider increasing the size of RPMSG_NAME_SIZE to 64? Have
> >>>>> you found cases where that wouldn't work?  I did a survey of all the
> >>>>> places the #define is used and all destination buffers are also using
> >>>>> the same #define in their definition.  It would also be backward
> >>>>> compatible with firmware implementations that use 32 byte.
> >>>>
> >>>> You can't directly bump the size without breaking the compatibility on
> >>>> the existing rpmsg_ns_msg in firmwares right? All the Linux-side drivers
> >>>> will be ok since they use the same macro but rpmsg_ns_msg has presence
> >>>> on both kernel and firmware-sides.
> >>>
> >>> Ah yes yes... The amount of bytes coming out of the pipe won't match.
> >>> Let me think a little...
> >>
> >> +1 for Suman's concern.
> >>
> >> Anyway i would like to challenge the need of more than 32 bytes to
> >> differentiate service instances.
> >> "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", seems to me enough if we only need
> >> to differentiate the instances.
>
> Remember that the rpmsg_device_id name takes some space within here. So,
> the shorter the rpmsg_device_id table name, the more room you have.
>
> >>
> >> But perhaps the need is also to provide a short description of the service?
>
> I am mostly using it to provide a unique instantiation name. In anycase,
> I have cross-checked against my current firmwares, and so far all of
> them happen to have the name + desc < 31 bytes.
>
>
> >>
> >> Suman, could you share some examples of your need?
> >
> > Looking at things further it is possible to extend the name of the service to
> > 64 byte while keeping backward compatibility by looking up the size of @len
> > in function rpmsg_ns_cb().  From there work with an rpmsg_ns_msg or a new
> > rpmsg_ns_msg64, pretty much the way you did in your patch[1].  In fact the
> > approach is the same except you are using 2 arrays of 32 byte and I'm using one
> > of 64.
> >
> > As Arnaud mentioned, is there an immediate need to support a 64-byte name?  If
> > not than I suggest to move forward with this patch and address the issue when we
> > get there - at least we know there is room for extention. Otherwise I'll spin
> > off another revision but it will be bigger and more complex.
>
> Yeah ok. I have managed to get my downstream drivers that use the desc
> field working with this patch after modifying the firmwares to publish
> using combined name, and adding logic in probe to get the trailing
> portion of the name.

Perfect

>
> So, the only thing that is missing or content for another patch is if we
> need to add some tooling/helper stuff for giving the trailing stuff to
> rpmsg drivers?

So that all rpmsg drivers don't come up with their own parsing that
ends up doing the same thing.  Let me think about that - I may have to
get back to you...

>
> regards
> Suman
>
> >
> > Thanks,
> > Mathieu
> >
> > [1]. https://patchwork.kernel.org/patch/11096599/
> >
> >>>>>>
> >>>>>>> ---
> >>>>>>> Changes for V2:
> >>>>>>> - Added Arnaud's Acked-by.
> >>>>>>> - Rebased to latest rproc-next.
> >>>>>>>
> >>>>>>>  drivers/rpmsg/rpmsg_core.c | 20 +++++++++++++++++++-
> >>>>>>>  1 file changed, 19 insertions(+), 1 deletion(-)
> >>>>>>>
> >>>>>>> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> >>>>>>> index e330ec4dfc33..bfd25978fa35 100644
> >>>>>>> --- a/drivers/rpmsg/rpmsg_core.c
> >>>>>>> +++ b/drivers/rpmsg/rpmsg_core.c
> >>>>>>> @@ -399,7 +399,25 @@ ATTRIBUTE_GROUPS(rpmsg_dev);
> >>>>>>>  static inline int rpmsg_id_match(const struct rpmsg_device *rpdev,
> >>>>>>>                                 const struct rpmsg_device_id *id)
> >>>>>>>  {
> >>>>>>> -     return strncmp(id->name, rpdev->id.name, RPMSG_NAME_SIZE) == 0;
> >>>>>>> +     size_t len = min_t(size_t, strlen(id->name), RPMSG_NAME_SIZE);
> >>>>>>> +
> >>>>>>> +     /*
> >>>>>>> +      * Allow for wildcard matches.  For example if rpmsg_driver::id_table
> >>>>>>> +      * is:
> >>>>>>> +      *
> >>>>>>> +      * static struct rpmsg_device_id rpmsg_driver_sample_id_table[] = {
> >>>>>>> +      *      { .name = "rpmsg-client-sample" },
> >>>>>>> +      *      { },
> >>>>>>> +      * }
> >>>>>>> +      *
> >>>>>>> +      * Then it is possible to support "rpmsg-client-sample*", i.e:
> >>>>>>> +      *      rpmsg-client-sample
> >>>>>>> +      *      rpmsg-client-sample_instance0
> >>>>>>> +      *      rpmsg-client-sample_instance1
> >>>>>>> +      *      ...
> >>>>>>> +      *      rpmsg-client-sample_instanceX
> >>>>>>> +      */
> >>>>>>> +     return strncmp(id->name, rpdev->id.name, len) == 0;
> >>>>>>>  }
> >>>>>>>
> >>>>>>>  /* match rpmsg channel and rpmsg driver */
> >>>>>>>
> >>>>>>
> >>>>
>