linux-kernel - Re: [PATCH] RTC: v3020 driver bugfix

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Date:	Tue, 3 Nov 2009 14:01:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	svalentine@...centris-systems.com
Cc:	rtc-linux@...glegroups.com, a.zummo@...ertech.it, raph@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RTC: v3020 driver bugfix

On Mon, 19 Oct 2009 15:11:23 -1000 (HST)
"Scott Valentine" <svalentine@...centris-systems.com> wrote:

> v3020 read_bit always returns 0 when left_shift > 7
> 
> The v3020 read_bit function's return type is (unsigned char). The code
> returns a value masked by (1 << left_shift) that is casted to the return
> type. If left_shift is larger than 7, the cast will always result in a 0
> return value. The problem was discovered with left_shift = 16, and the
> included patch corrects the problem.
> 
> The bug was introduced in the last (Apr 3 2009) commit of the file, kernel
> versions 2.6.30 and later.
> 
> diff -uNr a/drivers/rtc/rtc-v3020.c b/drivers/rtc/rtc-v3020.c
> --- a/drivers/rtc/rtc-v3020.c   2009-10-15 14:41:50.000000000 -1000
> +++ b/drivers/rtc/rtc-v3020.c   2009-10-19 14:06:27.000000000 -1000
> @@ -96,7 +96,7 @@
> 
>  static unsigned char v3020_mmio_read_bit(struct v3020 *chip)
>  {
> -       return readl(chip->ioaddress) & (1 << chip->leftshift);
> +       return ((readl(chip->ioaddress) & (1 << chip->leftshift)) != 0);
>  }
> 
>  static struct v3020_chip_ops v3020_mmio_ops = {

OK.

It's strange that the function returns `unsigned char' instead of say
int or bool.

We may as well do this in the same way as v3020_gpio_read_bit():

--- a/drivers/rtc/rtc-v3020.c~rtc-v3020-fix-v3020_mmio_read_bit
+++ a/drivers/rtc/rtc-v3020.c
@@ -96,7 +96,7 @@ static void v3020_mmio_write_bit(struct 
 
 static unsigned char v3020_mmio_read_bit(struct v3020 *chip)
 {
-	return readl(chip->ioaddress) & (1 << chip->leftshift);
+	return !!(readl(chip->ioaddress) & (1 << chip->leftshift));
 }
 
 static struct v3020_chip_ops v3020_mmio_ops = {
_


You didn't include a Signed-off-by: for this patch.
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