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

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

[Masahiro Yamada]

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().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.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)
-- 
1.9.1

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

[Peter Hurley]

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@socionext.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)
> 

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

[Masahiro Yamada]

Hi Peter,

2015-10-23 21:45 GMT+09:00 Peter Hurley <peter@hurleysoftware.com>:
> 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


OK, will do.


-- 
Best Regards
Masahiro Yamada