Re: [PATCH v3 0/3] IR driver for USB-UIRT device

[Johan Hovold <johan@kernel.org>]

Sorry about the late reply on this one.

On Fri, May 21, 2021 at 12:39:54PM +0100, Sean Young wrote:
> On Thu, May 20, 2021 at 03:31:34PM +0200, Johan Hovold wrote:
> > On Mon, May 17, 2021 at 11:35:22AM +0100, Sean Young wrote:
> > > On Mon, May 17, 2021 at 11:30:39AM +0200, Johan Hovold wrote:

> > > > Thanks for that pointer. Judging from a quick look, the new driver
> > > > appears to based on this one. By abstracting the serial interface bits
> > > > in a generic RC serdev/ldisc driver you may be able reuse more code,
> > > > even if I'm not in a position to judge how much of the IR protocol bits
> > > > that can be shared.
> > > 
> > > Yes, I agree. Once hotplugging is in place. If you have patches for that,
> > > please CC me and I can see if will work for IR drivers.
> > 
> > Let's hope someone steps up to fund that work then.
> 
> I'm just a volunteer. I've literally never heard anything about kernel work
> being funded by anyone.

Someone always pays whether it's a client, an employer or you yourself
with your spare time.

> Would you mind giving a brief summary what is needed to implement hotplugging
> for serdev? I get the impression it's not a lot of work, but I'm probably
> missing something obvious.

First, it's the matching bits we already touched on where we would like
to be able to use something like devicetree overlays to avoid rolling a
new mechanism for every bus. But devicetree overlays has its issues
currently (e.g. theres no user-space interface for providing them and
last time I checked they could not be reverted).

Second, serdev does not use the file abstraction and does not support
hangups which is used to implement tty hotplugging (e.g. by signalling
the consumer and making all file operations become noops after a
disconnect).

This would take some thinking-through to get right, and hopefully it can
be done without having to update every current serdev driver.

Retrofitting serdev into the tty layer wasn't painless and broke things
here and there. Supporting hotplugging should be doable but it's not as
straight-forward as it may sound.

Johan