linux-kernel - Re: [PATCH v7 10/13] serial: sh-sci: Add support for RZ/T2H SCI

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Message-ID: <2025041458-squint-dean-9999@gregkh>
Date: Mon, 14 Apr 2025 11:32:21 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Thierry Bultel <thierry.bultel@...atsea.fr>
Cc: Thierry Bultel <thierry.bultel.yh@...renesas.com>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	"geert@...ux-m68k.org" <geert@...ux-m68k.org>,
	Paul Barker <paul.barker.ct@...renesas.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v7 10/13] serial: sh-sci: Add support for RZ/T2H SCI

On Mon, Apr 14, 2025 at 11:23:34AM +0200, Thierry Bultel wrote:
> 
> 
> Le 14/04/2025 à 10:58, Greg KH a écrit :
> > On Mon, Apr 14, 2025 at 07:54:12AM +0000, Thierry Bultel wrote:
> > > Hi Greg,
> > > 
> > > > -----Original Message-----
> > > > From: Greg KH <gregkh@...uxfoundation.org>
> > > > Sent: vendredi 11 avril 2025 16:57
> > > > To: Thierry Bultel <thierry.bultel.yh@...renesas.com>
> > > > Cc: thierry.bultel@...atsea.fr; linux-renesas-soc@...r.kernel.org;
> > > > geert@...ux-m68k.org; Paul Barker <paul.barker.ct@...renesas.com>; Wolfram
> > > > Sang <wsa+renesas@...g-engineering.com>; linux-kernel@...r.kernel.org;
> > > > linux-serial@...r.kernel.org
> > > > Subject: Re: [PATCH v7 10/13] serial: sh-sci: Add support for RZ/T2H SCI
> > > > 
> > > > On Thu, Apr 03, 2025 at 11:29:12PM +0200, Thierry Bultel wrote:
> > > > > --- a/include/uapi/linux/serial_core.h
> > > > > +++ b/include/uapi/linux/serial_core.h
> > > > > @@ -231,6 +231,9 @@
> > > > >   /* Sunplus UART */
> > > > >   #define PORT_SUNPLUS	123
> > > > > 
> > > > > +/* SH-SCI */
> > > > > +#define PORT_RSCI	124
> > > > Why do you need to tell userspace about this specific port?  Is that a
> > > > hard requirement that your userspace tools require?  If not, please don't
> > > > export this here.
> > > This point has been discussed with Geert and Wolfram.
> > > We cannot use PORT_GENERIC for this IP, and adding the new type
> > > is just keeping consistent with the sh-sci driver.
> > But, why does userspace need to know this number?  And why doesn't
> > PORT_GENERIC work?
> 
> The reason is that the sh-sci driver discriminates internally between port
> types.
> There are number of locations when it checks for PORT_SCI, PORT_SCIF,
> PORT_SCIFA...

That is internal to the kernel, not external, right?

> T2H SCI needs special handling, too, that is the reason why PORT_GENERIC
> cannot work. I just therefore added this new type.

Again, why does userspace need to know this?

thanks,

greg k-h