[PATCH] dz: test after postfix decrement fails in dz_console_putchar()

[PATCH] dz: test after postfix decrement fails in dz_console_putchar()

[Roel Kluin]

When loops reaches 0 the postfix decrement still subtracts, so the test fails

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
---
diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c
index 116211f..0dddd68 100644
--- a/drivers/serial/dz.c
+++ b/drivers/serial/dz.c
@@ -819,7 +819,7 @@ static void dz_console_putchar(struct uart_port *uport, int ch)
 		dz_out(dport, DZ_TCR, mask);
 		iob();
 		udelay(2);
-	} while (loops--);
+	} while (--loops);
 
 	if (loops)				/* Cannot send otherwise. */
 		dz_out(dport, DZ_TDR, ch);

Re: [PATCH] dz: test after postfix decrement fails in dz_console_putchar()

[Maciej W. Rozycki]

On Wed, 9 Apr 2008, Roel Kluin wrote:

> When loops reaches 0 the postfix decrement still subtracts, so the test 
> fails

 You are right -- thanks for spotting it!

Acked-by: Maciej W. Rozycki <macro@linux-mips.org>

  Maciej

Re: [PATCH] dz: test after postfix decrement fails in dz_console_putchar()

[Johannes Weiner]

Hi,

Roel Kluin <12o3l@tiscali.nl> writes:

> When loops reaches 0 the postfix decrement still subtracts, so the test fails
>
> Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
> ---
> diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c
> index 116211f..0dddd68 100644
> --- a/drivers/serial/dz.c
> +++ b/drivers/serial/dz.c
> @@ -819,7 +819,7 @@ static void dz_console_putchar(struct uart_port *uport, int ch)
>  		dz_out(dport, DZ_TCR, mask);
>  		iob();
>  		udelay(2);
> -	} while (loops--);
> +	} while (--loops);

It will run loops + 1 times.  After your change it does run loops times.

>  	if (loops)				/* Cannot send otherwise. */
>  		dz_out(dport, DZ_TDR, ch);

The intention was probably that this gets executed if the break in the
loop (trdy == dport->port.line) is reached.  Without your fix, this
branch is also taken if the while-loop terminates with loops == -1
because of the postfix dec.

Your fix is correct but your changelog entry is wrong.

	Hannes

Re: [PATCH] dz: test after postfix decrement fails in dz_console_putchar()

[Maciej W. Rozycki]

On Wed, 9 Apr 2008, Johannes Weiner wrote:

> The intention was probably that this gets executed if the break in the
> loop (trdy == dport->port.line) is reached.  Without your fix, this
> branch is also taken if the while-loop terminates with loops == -1
> because of the postfix dec.

 You are right about the intention -- you cannot send a character to the 
transmitter unless the intended line has been reported as selected for 
transmission by the serial controller.  Otherwise it will go to the wrong 
line -- this is a serial multiplexer that selects transmission lines by 
itself.

 It used to be the other kind of a "while" loop.  This is a cut & paste 
bug -- I noticed the problem with the terminating condition of the loop 
and correctly moved it to the end, but forgot to adjust the 
decrementation.

> Your fix is correct but your changelog entry is wrong.

 s/fails/incorrectly succeeds/

  Maciej