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From:   Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Date:   Thu, 14 Jun 2018 17:20:40 +0200
Message-ID: <CAPybu_1ps+tEr5W_uvMSeH4_gwbjgKHnz0MoSEJO=Ut0a4sx6Q@mail.gmail.com>
Subject: Re: [PATCH v2 00/19] Dynamically load/remove serdev devices via sysfs*
To:     Johan Hovold <johan@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Rob Herring <robh@kernel.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>
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Hi Johan,
On Thu, Jun 14, 2018 at 4:55 PM Johan Hovold <johan@kernel.org> wrote:
>
> On Thu, Jun 14, 2018 at 04:06:18PM +0200, Ricardo Ribalda Delgado wrote:
> > Hi Johan,
> > On Thu, Jun 14, 2018 at 3:34 PM Johan Hovold <johan@kernel.org> wrote:
>
> > > And there are more issues with the series which are less apparent than
> > > the rx (and partial tx) regression.
> >
> > Any hints about this? What else should I change on the series?
>
> There are implementation issues and there's the more fundamental
> question about whether your approach to this is the right one.
>
> Like Rob, I'm not sure we want to have the device topology depend on a
> kernel config symbol (serdev and your ttydev driver). We may need to
> explore Rob's sibling-device idea further.

From my point of view, if the user enables serdev, then everything has
to be a serdev, because serdev does not provide the same functionality
as a core tty device I had to implement, serdev-ttydev.c. Which is
nothing more than a wrapper.

It is very hacky, but allows replacing the core tty device with another serdev.

>
> I also want to make sure that this can be used for discoverable buses
> (e.g. the USB CEC device the I've used as an example before).
>

I have tried your patch:

https://github.com/ribalda/linux/commit/5cb30b4ce6477132a23492c674d8b3dc81ecff86

the only issue is that the serdev device sometimes explotes (OOPS)
when the usb is unplugged :S.

And that might be quite tricy to solve

> As for the current implementation there are both larger and smaller
> issues, like for example:
>
>  - the fact that your sysfs and lookup interface does not use any
>    locking whatsoever and thus is susceptible to races

I thought that sysfs access where serialised. If that is not the case
yes, we need a lock.

>
>  - your ttyport driver currently breaks the sysfs interface for all
>    serial (core) devices by ignoring the attribute groups

Yep, you are right, I screwed up that one :).

>
>  - the ttyport driver is arguably a hack with layering issues (which
>    admittedly may be hard to avoid given the retrofitting of serdev into
>    the tty layer)
>
> Again, I suggest you submit a subset of your series (aim at 10 patches
> or so) as an RFC which can be used as a basis for further discussion. No
> point in discussing every implementation detail if the underlying
> approach needs to be revised.

Will do. Give me some time to give it a hand of paint.

Thanks for time reviewing my little moster

>
> > > It's legacy as in old, and to be used for one-off hacks and such. But
> > > sure, that is also what this series aims at even if that doesn't mean
> > > you *have to* copy the interface.
> >
> > It is not only one-off hack. It is the ONLY way to use i2c devices
> > that are not enumerated.
> >
> > The same way as today we do not have any way of using serdev on non
> > enumerated devices.
>
> You're missing the point: none of that means you have to copy the
> interface.
>
> Johan


-- 
Ricardo Ribalda