linux-kernel - Re: [PATCH] [media] ov2640: add support for async device registration

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Message-id: <532AFED3.5030103@samsung.com>
Date:	Thu, 20 Mar 2014 15:44:35 +0100
From:	Sylwester Nawrocki <s.nawrocki@...sung.com>
To:	Josh Wu <josh.wu@...el.com>
Cc:	g.liakhovetski@....de, m.chehab@...sung.com,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [media] ov2640: add support for async device registration

Hi Josh,

On 19/03/14 10:17, Josh Wu wrote:
> On 3/15/2014 5:17 AM, Sylwester Nawrocki wrote:
>> > On 03/14/2014 11:12 AM, Josh Wu wrote:
>>> >> +    clk = v4l2_clk_get(&client->dev, "mclk");
>>> >> +    if (IS_ERR(clk))
>>> >> +        return -EPROBE_DEFER;
>> >
>> > You should instead make it:
>> >
>> >         return PTR_ERR(clk);
>> >
>> > But you will need this patch for that to work:
>> > http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/drivers/clk/clk.c?id=a34cd4666f3da84228a82f70c94b8d9b692034ea 
>> >
>> >
>> > With this patch there is no need to overwrite any returned error
>> > value with EPROBE_DEFER.
>
> Thanks for the information. I will use this in v2 version.

Oops, I missed somehow that it's v4l2_clk_get(), rather than
clk_get(). So it seems it will not work when you return PTR_ERR(clk),
since v4l2_clk_get() returns -ENODEV when clock is not found.
I think we should modify v4l2_clk_get() so it returns EPROBE_DEFER
rather than ENODEV on error. I anticipate v4l2_clk_get() might be
using clk_get() internally in future, and the v4l2 clk look up
will be used as a fallback only. So sensor drivers should just
do something like:

 clk = v4l2_clk_get(...);
 if (IS_ERR(clk))
	return PTR_ERR(clk);

--
Regards,
Sylwester
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