linux-kernel - Re: [PATCH 0/3] USB-Serial serdev support

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Message-ID: <20241028225702.tdtfqzhm335vvuv5@pengutronix.de>
Date: Mon, 28 Oct 2024 23:57:02 +0100
From: Marco Felsch <m.felsch@...gutronix.de>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Rob Herring <robh@...nel.org>, Jiri Slaby <jirislaby@...nel.org>,
	Johan Hovold <johan@...nel.org>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 0/3] USB-Serial serdev support

Hi Greg,

On 24-10-01, Greg Kroah-Hartman wrote:
> On Tue, Oct 01, 2024 at 09:24:53AM +0200, Marco Felsch wrote:
> > Hi,
> > 
> > gentle ping as this is series is two months old now.
> 
> And it was rejected as serdev does not support hotplug which of course,
> usb-serial does.

I hoped to get some feedback on my answer [1]. Regarding hotplug
support: serdev _requires_ some sort of firmware like OF (not sure if it
does work with ACPI too). That said, if serdev finds no firmware a
fallback is provided to the standard serial handling.

The firmware could either be added directly by the platform OF file or
via OF-overlays. By making use of overlays we could gain some kind of
hotplug: Once a usb devices was detected and the driver has an
overlay, the overlay gets applied and the probe continues, like we do it
for PCIe devices now [2]. For devices which don't have a registered
overlay the standard usb-serial setup is done by exposing the serial
interface to the userspace.

> So until serdev is fixed up to handle that correctly, this is not going
> anywhere, nor should you want it to as then you would be in charge of
> code that does not work properly :)

Regards,
  Marco

[1] https://lore.kernel.org/all/20240917044948.i2eog4ondf7vna7q@pengutronix.de/
[2] https://lore.kernel.org/all/7512cbb7911b8395d926e9e9e390fbb55ce3aea9.camel@pengutronix.de/

> 
> thanks,
> 
> greg k-h
>