linux-kernel - Re: How does commit 47ec340c not introduce a bug?

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Message-ID: <CAN1soZyHx1XZzukunbKsj+v4h93MRQKjPPjJ3+i3u8BeBbhCGw@mail.gmail.com>
Date:	Tue, 7 May 2013 17:35:28 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Robin Holt <holt@....com>, Qing Xu <qingx@...vell.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: How does commit 47ec340c not introduce a bug?

On Tue, May 7, 2013 at 5:24 PM, Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
> Hello,
>
> On Tue, May 07, 2013 at 04:17:34AM -0500, Robin Holt wrote:
>> I noticed a warning while cross-compiling all arm defconfigs.
>>
>> The mmp2_defconfig gave this warning:
>>
>> drivers/video/backlight/max8925_bl.c: In function 'max8925_backlight_probe':
>> drivers/video/backlight/max8925_bl.c:177:3: warning: statement with no effect [-Wunused-value]
>>
>> This appears to have been introduced by the above commit when !CONFIG_OF
>>
>> Looking at this more closely, I am not sure how this was ever intended
>> to be handled or how the errors returned in the CONFIG_OF case were
>> intended to be handled as the return from max8925_backlight_dt_init is
>> always ignored.
>>
>> I think this needs some more attention, but do not feel like I know
>> enough about it or have any means to test it to weigh in.
>>
>> Thanks,
>> Robin
>>
>>
>> commit 47ec340cb8e232671e7c4a4689ff32c3bdf329da
>> Author: Qing Xu <qingx@...vell.com>
>> Date:   Mon Feb 4 23:40:45 2013 +0800
>>
>>     mfd: max8925: Support dt for backlight
>>
>>     Add device tree support in max8925 backlight.
>>
>>     Signed-off-by: Qing Xu <qingx@...vell.com>
>>     Signed-off-by: Haojian Zhuang <haojian.zhuang@...il.com>
>>     Signed-off-by: Samuel Ortiz <sameo@...ux.intel.com>
>>
>> diff --git a/drivers/video/backlight/max8925_bl.c b/drivers/video/backlight/max8925_bl.c
>> index 2c9bce0..5ca11b0 100644
>> --- a/drivers/video/backlight/max8925_bl.c
>> +++ b/drivers/video/backlight/max8925_bl.c
>> @@ -101,6 +101,29 @@ static const struct backlight_ops max8925_backlight_ops = {
>>       .get_brightness = max8925_backlight_get_brightness,
>>  };
>>
>> +#ifdef CONFIG_OF
>> +static int max8925_backlight_dt_init(struct platform_device *pdev,
>> +                           struct max8925_backlight_pdata *pdata)
>> +{
>> +     struct device_node *nproot = pdev->dev.parent->of_node, *np;
>> +     int dual_string;
>> +
>> +     if (!nproot)
>> +             return -ENODEV;
>> +     np = of_find_node_by_name(nproot, "backlight");
>> +     if (!np) {
>> +             dev_err(&pdev->dev, "failed to find backlight node\n");
>> +             return -ENODEV;
>> +     }
>> +
>> +     of_property_read_u32(np, "maxim,max8925-dual-string", &dual_string);
>> +     pdata->dual_string = dual_string;
>> +     return 0;
>> +}
>> +#else
>> +#define max8925_backlight_dt_init(x, y)      (-1)
> It's probably best to make this:
>
> static inline max8925_backlight_dt_init(struct platform_device *pdev,
>                                 struct max8925_backlight_pdata *pdata)
> {
>         return -ENODEV;
> }
>

I've submitted this patch to fix this issue for a long time.

Samuel,

Should I send it again?

Regards
Haojian
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