Re: [PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver support

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jun 13, 2023 at 05:44:23PM +0200, Arnd Bergmann wrote:
> On Tue, Jun 13, 2023, at 16:49, Greg KH wrote:
> > On Tue, Jun 13, 2023 at 06:58:32PM +0800, Jacky Huang wrote:
> >> 
> >> On 2023/6/13 下午 06:28, Greg KH wrote:
> >> > On Mon, Jun 12, 2023 at 02:53:55AM +0000, Jacky Huang wrote:
> >> > > From: Jacky Huang <ychuang3@nuvoton.com>
> >> > > 
> >> > > This adds UART and console driver for Nuvoton ma35d1 Soc.
> >> > > It supports full-duplex communication, FIFO control, and
> >> > > hardware flow control.
> >> > You get a full 72 columns for your changelog :)
> >> > 
> >> > > --- a/include/uapi/linux/serial_core.h
> >> > > +++ b/include/uapi/linux/serial_core.h
> >> > > @@ -279,4 +279,7 @@
> >> > >   /* Sunplus UART */
> >> > >   #define PORT_SUNPLUS	123
> >> > > +/* Nuvoton MA35 SoC */
> >> > > +#define PORT_MA35	124
> >> > > +
> >> > Why is this change needed?  What userspace code is going to rely on it?
> >> > 
> >> > thanks,
> >> > 
> >> > greg k-h
> >> 
> >> Because the serial driver requires a port->type, and almost all serial
> >> drivers defined their port type here. We follow the practice of most serial
> >> drivers here.
> >> If we don't do it this way, we would have to directly assign a value to
> >> port->type. However, such modifications were questioned in the past,
> >> which is why we changed it back to defining the port type in serial_core.h.
> >
> > I really really want to get rid of this list, as it's a UAPI that no one
> > uses.  So please don't use it, it doesn't help anything, and while the
> > serial driver might require it, it doesn't actually do anything with
> > that field, right?  So why don't we just set all of the values to the
> > same one?
> 
> I don't see how Jacky can come up with a patch to do this correctly
> without more specific guidance to what exactly you are looking for,
> after the last 123 people that added support for a new port got
> that merged.

I keep complaining about this, when I notice it.  Just use the "default"
port type in the serial driver and don't add a new type here and it
should just work, right?

> I checked debian codesearch and found only three obscure packages that
> accidentally include this header instead of including linux/serial.h,
> a couple of lists of all kernel headers, and none that include it on
> purpose. I agree that this header should really not exist in uapi,
> but the question is what exactly to do about it.
> 
> Possible changes would be:
> 
> - add a special value PORT_* constant other than PORT_UNKNOWN that
>   can be used by serial drivers instead of a unique value, and
>   ensure that the serial core can handle drivers using it.

Why do we need a special constant?

> - move all values used by the 8250 driver from serial_core.h
>   to serial.h, as this driver actually uses the constants.

Makes sense.

> - Move the remaining contents of uapi/linux/serial.h into the 
>   non-uapi version.
> 
> - Change all drivers that only reference a single PORT_*
>   value to use the generic one.

I think this is the best thing to do.

thanks,

greg k-h

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