linux-kernel - Re: [alsa-devel] regression v4.16 on Nokia N900: sound does not work

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Date:   Fri, 2 Mar 2018 11:18:10 -0600
From:   "Andrew F. Davis" <afd@...com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
CC:     Pavel Machek <pavel@....cz>,
        Linus Walleij <linus.walleij@...aro.org>,
        Martijn Braam <martijn@...xit.nl>,
        Daniel Baluta <daniel.baluta@...il.com>,
        Ivajlo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        ext Tony Lindgren <tony@...mide.com>,
        Mark Brown <broonie@...nel.org>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Pali Rohár <pali.rohar@...il.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Filip Matijević <filip.matijevic.pz@...il.com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Mickuláš Qwertz <abcloriens@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Sebastian Reichel <sre@...nel.org>, <clayton@...ftyguy.net>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Patrik Bachan <patrikbachan@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        <serge@...lyn.com>
Subject: Re: [alsa-devel] regression v4.16 on Nokia N900: sound does not work

On 03/02/2018 11:08 AM, Russell King - ARM Linux wrote:
> On Fri, Mar 02, 2018 at 08:22:52AM -0600, Andrew F. Davis wrote:
>>> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
>>> index 84e5a9d..f0fab26 100644
>>> --- a/drivers/gpio/gpiolib-of.c
>>> +++ b/drivers/gpio/gpiolib-of.c
>>> @@ -241,29 +241,17 @@ struct gpio_desc *of_find_gpio(struct device *dev, const char *con_id,
>>>  
>>>  		desc = of_get_named_gpiod_flags(dev->of_node, prop_name, idx,
>>>  						&of_flags);
>>> -		/*
>>> -		 * -EPROBE_DEFER in our case means that we found a
>>> -		 * valid GPIO property, but no controller has been
>>> -		 * registered so far.
>>> -		 *
>>> -		 * This means we don't need to look any further for
>>> -		 * alternate name conventions, and we should really
>>> -		 * preserve the return code for our user to be able to
>>> -		 * retry probing later.
>>> -		 */
>>> -		if (IS_ERR(desc) && PTR_ERR(desc) == -EPROBE_DEFER)
>>> -			return desc;
>>>  
>>> -		if (!IS_ERR(desc) || (PTR_ERR(desc) != -ENOENT))
>>> +		if (!IS_ERR(desc) || PTR_ERR(desc) != -ENOENT)
>>
>>
>> I rather like the () so one doesn't always have to look up C operator
>> precedence to verify..
> 
> Too many make it impossible to see which close paren ties up with
> which open paren.  I've spent way too long in the past reformatting
> code, where people think that () are a good thing, to work out what
> the comparison is actually doing before then rewriting the damn
> thing with less () and in a much clearer way.  I'm now convinced
> that unnecessary () are a very bad thing as they severely harm
> readability as test complexity increases.
> 


Fair enough, I personally prefer always having a new line per condition
when doing chained conditionals:

if (something &&
    this == that &&
    !not_this)


>>
>>
>>>  			break;
>>>  	}
>>>  
>>>  	/* Special handling for SPI GPIOs if used */
>>> -	if (IS_ERR(desc))
>>> +	if (IS_ERR(desc) && PTR_ERR(desc) == -ENOENT)
> 
> These can be simplified to:
> 
> 	if (desc == ERR_PTR(-ENOENT))
> 
> since error pointers are unique - ERR_PTR(-ENOENT) is what was
> returned as an error-pointer, and if IS_ERR(ERR_PTR(-ENOMENT)) etc
> were false, we'd have big problems as it'd mean we couldn't detect
> error pointers!
> 
> As an added bonus, they don't involve any operator precedence
> questions either.
> 

Looks like your suggestion clears up this one anyway.