linux-kernel - Re: [PATCH] serial: 8250_dw: always set baud rate in dw8250_set

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Message-ID: <c8d4ea3577c1ac492b977ea10145a7c76630d5a7.camel@linux.intel.com>
Date:   Fri, 27 Jul 2018 14:00:25 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Chen Hu <hu1.chen@...el.com>, andy.shevchenko@...il.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Subramony Sesha <subramony.sesha@...el.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Stefan Potyra <Stefan.Potyra@...ktrobit.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Archana Patni <archana.patni@...el.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: 8250_dw: always set baud rate in
 dw8250_set_termios

On Fri, 2018-07-27 at 18:32 +0800, Chen Hu wrote:
> dw8250_set_termios() doesn't set baud rate if the arg "old ktermios"
> is
> NULL. This happens during resume.
> Call Trace:
> ...
> [   54.928108] dw8250_set_termios+0x162/0x170
> [   54.928114] serial8250_set_termios+0x17/0x20
> [   54.928117] uart_change_speed+0x64/0x160
> [   54.928119] uart_resume_port
> ...
> 
> So the baud rate is not restored after S3 and breaks the apps who use
> UART, for example, console and bluetooth etc.
> 
> We address this issue by setting the baud rate irrespective of arg
> "old", just like the drivers for other 8250 IPs. This is tested with
> Intel Broxton platform.

You forgot to add

Fixes: 4e26b134bd17 ("serial: 8250_dw: clock rate handling for all ACPI
platforms")
Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

The change itself LGTM,

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> 
> Signed-off-by: Chen Hu <hu1.chen@...el.com>
> ---
> We found UART based apps such as console and bluetooth etc. are broken
> after S3
> on Intel Broxton platform. The further debug shows that the baud rate
> of all
> UARTs are different with our settings after S3. During S3, the 8250
> related IPs
> may lose power and thus lose the OS's baud rate setting. The driver
> should
> restore it during resume. However, Desinware 8250's driver doesn't
> restore the
> baud if the arg "old ktermios" is NULL. Unfortunely, it get a NULL arg
> from
> serial_core and skips this step in resume path.
> 
> Andy guide me that he doesn't see other 8250 IPs judge old==NULL to
> set baud.
> 
> With the modification in this email, the baud rate is OK after S3. A
> local
> quick test doesn't show any error. Report the issue here and hope some
> serial
> experts can present formal patch to fix.
>  drivers/tty/serial/8250/8250_dw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c
> b/drivers/tty/serial/8250/8250_dw.c
> index 02a9b995e8f9..82bf46507f6d 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -250,7 +250,7 @@ static void dw8250_set_termios(struct uart_port
> *p, struct ktermios *termios,
>  	long rate;
>  	int ret;
>  
> -	if (IS_ERR(d->clk) || !old)
> +	if (IS_ERR(d->clk))
>  		goto out;
>  
>  	clk_disable_unprepare(d->clk);

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy