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

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Message-ID: <2025010602-cozily-rind-c2c6@gregkh>
Date: Mon, 6 Jan 2025 14:44:53 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Sherry Sun <sherry.sun@....com>
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

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.)

> This patch just refers to many other uart driver patches to extend
> maximum uart number, such as
> https://lore.kernel.org/all/20240112095300.2004878-3-valentin.caron@foss.st.com/.
> Agree that it will be nice to dynamically allocate everything, but for
> now I prefer to simply change this value as there doesn't seem to be a
> good uart implementation at the moment, not sure what you prefer?  :)

I'd prefer not hard-coding stuff like this but if it's going to be too
much of a pain I guess I'll take this for now...

thanks,

greg k-h