linux-kernel - Re: [PATCH] clk: prevent __of_clk_get_hw_from

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Date:	Wed, 10 Aug 2016 17:16:29 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-clk <linux-clk@...r.kernel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: prevent __of_clk_get_hw_from_provider() from
 returning NULL

2016-08-05 5:57 GMT+09:00 Stephen Boyd <sboyd@...eaurora.org>:
> On 07/19, Masahiro Yamada wrote:
>> The .get(_hw) callback of an OF clock provider can return a NULL
>> pointer in some cases.
>>
>> For example, of_clk_src_onecell_get() returns NULL for index 1 of a
>> sparse array of clocks like follows:
>>
>>   clk_num == 3
>>   idx 0: UART clk
>>   idx 1: NULL (no clk is allocated)
>>   idx 2: I2C clk
>>
>> In such cases, clk_get() successfully returns NULL.
>>
>> A problem is that most drivers only check IS_ERR(), like follows:
>>
>>   clk = devm_clk_get(dev, NULL);
>>   if (IS_ERR(clk))
>>           return PTR_ERR(clk);
>>
>> It carries on moving forward and will probably be hit by a different
>> error check with a different error message.
>
> NULL is a valid clk pointer, so we can't really do anything here
> besides rely on driver authors to do the right thing.


I still do not understand this.


I think clk_get() should return > 0 pointer on success,
error-pointer on failure.

I have no idea when NULL is useful as a return value of clk_get().




-- 
Best Regards
Masahiro Yamada