linux-kernel - Re: [PATCH] serial: 8250_early: do not save and restore IER in write callback

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Message-ID: <562A2C01.4070006@hurleysoftware.com>
Date:	Fri, 23 Oct 2015 08:45:53 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	linux-serial@...r.kernel.org
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Kevin Cernekee <cernekee@...il.com>,
	Jiri Slaby <jslaby@...e.com>, Rob Herring <robh@...nel.org>,
	linux-kernel@...r.kernel.org,
	Eddie Huang <eddie.huang@...iatek.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] serial: 8250_early: do not save and restore IER in write
 callback

On 10/22/2015 04:21 AM, Masahiro Yamada wrote:
> The IER has already been masked in early_serial8250_setup(), there is
> no reason to save and restore it every time early_serial8250_write()
> is called.
> 
> Let wait_for_xmitr() melt into serial_putc().

Both of these changes are ok with me, but please split this into
2 patches so reverting either one in case of regression is trivial.

Regards,
Peter Hurley

> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
>  drivers/tty/serial/8250/8250_early.c | 20 ++------------------
>  1 file changed, 2 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> index 7aff3d8..19aca19 100644
> --- a/drivers/tty/serial/8250/8250_early.c
> +++ b/drivers/tty/serial/8250/8250_early.c
> @@ -76,21 +76,17 @@ static void __init serial8250_early_out(struct uart_port *port, int offset, int
>  
>  #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
>  
> -static void __init wait_for_xmitr(struct uart_port *port)
> +static void __init serial_putc(struct uart_port *port, int c)
>  {
>  	unsigned int status;
>  
>  	for (;;) {
>  		status = serial8250_early_in(port, UART_LSR);
>  		if ((status & BOTH_EMPTY) == BOTH_EMPTY)
> -			return;
> +			break;
>  		cpu_relax();
>  	}
> -}
>  
> -static void __init serial_putc(struct uart_port *port, int c)
> -{
> -	wait_for_xmitr(port);
>  	serial8250_early_out(port, UART_TX, c);
>  }
>  
> @@ -99,20 +95,8 @@ static void __init early_serial8250_write(struct console *console,
>  {
>  	struct earlycon_device *device = console->data;
>  	struct uart_port *port = &device->port;
> -	unsigned int ier;
> -
> -	/* Save the IER and disable interrupts preserving the UUE bit */
> -	ier = serial8250_early_in(port, UART_IER);
> -	if (ier)
> -		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
>  
>  	uart_console_write(port, s, count, serial_putc);
> -
> -	/* Wait for transmitter to become empty and restore the IER */
> -	wait_for_xmitr(port);
> -
> -	if (ier)
> -		serial8250_early_out(port, UART_IER, ier);
>  }
>  
>  static void __init init_port(struct earlycon_device *device)
> 

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