linux-kernel - Re: [PATCH v4 5/5] drivers/tty/serial: add ESP32S3 ACM device driver

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Date:   Fri, 6 Oct 2023 09:11:15 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Max Filippov <jcmvbkbc@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        devicetree@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH v4 5/5] drivers/tty/serial: add ESP32S3 ACM device driver

On Tue, Oct 3, 2023 at 2:47 PM Max Filippov <jcmvbkbc@...il.com> wrote:
>
> On Tue, Oct 3, 2023 at 5:55 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Thu, Sep 28, 2023 at 08:16:31AM -0700, Max Filippov wrote:
> > > Add driver for the ACM  controller of the Espressif ESP32S3 Soc.
> >
> > Odd extra space :(
>
> Ok.
>
> > > Hardware specification is available at the following URL:
> > >
> > >   https://www.espressif.com/sites/default/files/documentation/esp32-s3_technical_reference_manual_en.pdf
> > >   (Chapter 33 USB Serial/JTAG Controller)
> >
> > I don't understand this driver, "ACM" is a USB host <-> gadget protocol,
> > why do you need a platform serial driver for this?
>
> The USB part of this piece of hardware is fixed and not controllable, so
> all we have is a very limited UART interface. But to the outside world
> it's a USB device with the CDC-ACM interface.
>
> > > diff --git a/drivers/tty/serial/esp32_acm.c b/drivers/tty/serial/esp32_acm.c
> > > new file mode 100644
> > > index 000000000000..f02abd2ac65e
> > > --- /dev/null
> > > +++ b/drivers/tty/serial/esp32_acm.c
> > > @@ -0,0 +1,459 @@
> > > +// SPDX-License-Identifier: GPL-2.0-or-later
> >
> > Why "or later"?  I have to ask, sorry.
>
> I don't really have a preference here. Is there a reason to choose
> GPL-2.0 only for a new code?

Yes, that's the default license for the kernel. So you should have a
reason for picking something else. Like maybe you copied all this from
somewhere else and that was the license.

Rob