linux-kernel - RE: [PATCH] tty: serial: fsl_lpuart: increase maximum uart

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Message-ID:
 <DB9PR04MB84290597CC2BA6CFA096849B92112@DB9PR04MB8429.eurprd04.prod.outlook.com>
Date: Tue, 7 Jan 2025 08:29:12 +0000
From: Sherry Sun <sherry.sun@....com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: "jirislaby@...nel.org" <jirislaby@...nel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: RE: [PATCH] tty: serial: fsl_lpuart: increase maximum uart_nr to 12



> -----Original Message-----
> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: Monday, January 6, 2025 9:45 PM
> To: Sherry Sun <sherry.sun@....com>
> Cc: jirislaby@...nel.org; linux-serial@...r.kernel.org; linux-
> kernel@...r.kernel.org; imx@...ts.linux.dev
> Subject: Re: [PATCH] tty: serial: fsl_lpuart: increase maximum uart_nr to 12
> 
> On Mon, Jan 06, 2025 at 10:24:52AM +0000, Sherry Sun wrote:
> >
> >
> > > -----Original Message-----
> > > From: Greg KH <gregkh@...uxfoundation.org>
> > > Sent: Friday, January 3, 2025 5:08 PM
> > > To: Sherry Sun <sherry.sun@....com>
> > > Cc: jirislaby@...nel.org; linux-serial@...r.kernel.org; linux-
> > > kernel@...r.kernel.org; imx@...ts.linux.dev
> > > Subject: Re: [PATCH] tty: serial: fsl_lpuart: increase maximum
> > > uart_nr to 12
> > >
> > > On Fri, Jan 03, 2025 at 03:11:54PM +0800, Sherry Sun wrote:
> > > > Some SoCs like the i.MX943 have aliases for up to 12 UARTs, need
> > > > to increase UART_NR from 8 to 12 to support lpuart9-12 to avoid
> > > > initialization failures.
> > > >
> > > > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > > > ---
> > > >  drivers/tty/serial/fsl_lpuart.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > > > b/drivers/tty/serial/fsl_lpuart.c index 57b0632a3db6..7cb1e36fdaab
> > > > 100644
> > > > --- a/drivers/tty/serial/fsl_lpuart.c
> > > > +++ b/drivers/tty/serial/fsl_lpuart.c
> > > > @@ -245,7 +245,7 @@
> > > >
> > > >  #define DRIVER_NAME	"fsl-lpuart"
> > > >  #define DEV_NAME	"ttyLP"
> > > > -#define UART_NR		8
> > > > +#define UART_NR		12
> > >
> > > Why not fix this properly and make this dynamic and get rid of the
> > > static array causing all of this problem?  That way when you get a
> > > system with 13 uarts, you will be ok :)
> > >
> >
> > Hi Greg,
> >
> > Thanks for your comment.
> > But I checked all the uart drivers under drivers/tty/serial/, UART_NR
> > is widely used, currently almost every uart driver that supports
> > multiple uart ports defines this macro, this value is needed for the
> > nr parameter of struct uart_driver, also for console index checking
> > and setup.
> 
> Yeah, it's messy, but it can be done (for example see all of the usb-serial
> devices, we don't limit the number of those ports in the system except to 256
> I think.)

BTW, it seems that usb-serial devices also have the max ports limit, you can
check the MAX_NUM_PORTS macro in include/linux/usb/serial.h, it was extended from 8 to 16 now.

/* The maximum number of ports one device can grab at once */
#define MAX_NUM_PORTS       16

Best Regards
Sherry