linux-kernel - Re: [PATCH] backlight: Fix the logic to set bits in adp8860_bl and adp8870

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Message-Id: <20120113141019.1fc1439e.akpm@linux-foundation.org>
Date:	Fri, 13 Jan 2012 14:10:19 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Axel Lin <axel.lin@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Michael Hennerich <michael.hennerich@...log.com>,
	Richard Purdie <rpurdie@...ys.net>,
	device-drivers-devel@...ckfin.uclinux.org
Subject: Re: [PATCH] backlight: Fix the logic to set bits in adp8860_bl and
 adp8870_bl drivers

On Fri, 13 Jan 2012 16:15:21 +0800
Axel Lin <axel.lin@...il.com> wrote:

> We need to write new value if the bit mask fields of new value is not equal to
> old value. It does not make sense to write new value only when all the bit_mask
> bits are zero.

When fixing bugs, please always describe the user-visible effects of
the bug.

> diff --git a/drivers/video/backlight/adp8860_bl.c b/drivers/video/backlight/adp8860_bl.c
> index 66bc74d..378276c 100644
> --- a/drivers/video/backlight/adp8860_bl.c
> +++ b/drivers/video/backlight/adp8860_bl.c
> @@ -146,7 +146,7 @@ static int adp8860_set_bits(struct i2c_client *client, int reg, uint8_t bit_mask
>  
>  	ret = adp8860_read(client, reg, &reg_val);
>  
> -	if (!ret && ((reg_val & bit_mask) == 0)) {
> +	if (!ret && ((reg_val & bit_mask) != bit_mask)) {
>  		reg_val |= bit_mask;
>  		ret = adp8860_write(client, reg, reg_val);
>  	}
> diff --git a/drivers/video/backlight/adp8870_bl.c b/drivers/video/backlight/adp8870_bl.c
> index 6c68a68..6735059 100644
> --- a/drivers/video/backlight/adp8870_bl.c
> +++ b/drivers/video/backlight/adp8870_bl.c
> @@ -160,7 +160,7 @@ static int adp8870_set_bits(struct i2c_client *client, int reg, uint8_t bit_mask
>  
>  	ret = adp8870_read(client, reg, &reg_val);
>  
> -	if (!ret && ((reg_val & bit_mask) == 0)) {
> +	if (!ret && ((reg_val & bit_mask) != bit_mask)) {
>  		reg_val |= bit_mask;
>  		ret = adp8870_write(client, reg, reg_val);
>  	}

This patch is applicable to 3.2.x, but I don't know whether to route it
to -stable becasue you didn't tell me what effect the patch has :(

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