linux-kernel - Re: [PATCH 13/16] regulator: mc13xxx: Use of_get_child_by

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Message-ID: <CAK9yfHyAK+LtQLr_b-OLHa63dSNT5KN7MBHxqVoTbiHVb4-7DA@mail.gmail.com>
Date:	Mon, 24 Feb 2014 20:40:27 +0530
From:	Sachin Kamat <sachin.kamat@...aro.org>
To:	Philippe Rétornaz <philippe.retornaz@...l.ch>
Cc:	Mark Brown <broonie@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH 13/16] regulator: mc13xxx: Use of_get_child_by_name

On 24 February 2014 20:37, Philippe Rétornaz <philippe.retornaz@...l.ch> wrote:
> Le 24/02/2014 15:51, Sachin Kamat a écrit :
>
>> On 24 February 2014 19:14, Philippe Rétornaz
>> <philippe.retornaz@...l.ch> wrote:
>>>
>>> Hi
>>>
>>> This patch breaks DT-Enabled kernel run on non-DT board: [
>>> 0.822977] Unable to handle kernel NULL pointer dereference at
>>> virtual address 0000001c (...) [    0.880320] [<c02f3e94>]
>>> (of_get_next_child) from [<c02f5420>]
>>> (of_get_child_by_name+0x38/0x50) [    0.881449] [<c02f5420>]
>>> (of_get_child_by_name) from [<c01f6258>]
>>> (mc13xxx_get_num_regulators_dt+0x18/0x64) [    0.882707]
>>> [<c01f6258>] (mc13xxx_get_num_regulators_dt) from [<c01f5d38>]
>>> (mc13783_regulator_probe+0x34/0x17c) [    0.884011] [<c01f5d38>]
>>> (mc13783_regulator_probe) from [<c021fed0>]
>>> (platform_drv_probe+0x20/0x54) [    0.885182] [<c021fed0>]
>>> (platform_drv_probe) from [<c021e674>]
>>> (driver_probe_device+0x144/0x360) (...)
>>>
>>> Because mc13783-regulator do in its probe: static int
>>> mc13783_regulator_probe(struct platform_device *pdev) { (...) int
>>> i, num_regulators;
>>>
>>> num_regulators = mc13xxx_get_num_regulators_dt(pdev); if
>>> (num_regulators <= 0 && pdata) num_regulators =
>>> pdata->num_regulators
>>>
>>>
>>> and mc13xxx_get_num_regulators_dt() do, before your patch:
>>>
>>> parent = of_find_node_by_name(pdev->dev.parent->of_node,
>>> "regulators"); if (!parent) return -ENODEV;
>>>
>>> of_find_node_by_name will return NULL if the node passed is NULL
>>> and the DT is non-existant.
>>>
>>> But, with your change we use this: parent =
>>> of_get_child_by_name(pdev->dev.parent->of_node, "regulators");
>>>
>>> Which will OOPS as it does not expect to have a NULL node passed as
>>> argument.
>>>
>>> So please revert this patch.
>>
>>
>> Sorry for the issue caused due to this patch. I would prefer to try
>> to have this fixed before reverting. Can you please try with below
>> change and let me know if it works:
>>
>> parent = of_get_child_by_name(pdev->dev->of_node, "regulators");
>>
>
> You meant pdev->dev.of_node here I guess ?

Yes right. Sorry for the typo.

> This still OOPS as the board is not booting with DT, so all of_node are
> NULL.

So this is non-DT mode. Please see further comments below.

>
>> Also, how about adding NULL check to see it the node exists at all?
>>
>
> Could be an option. BTW, mc13xxx_parse_regulators_dt() has the same problem.

I would suggest adding a check at the initial stage itself to see if
it is non-DT and then either
error out or skip appropriately.

-- 
With warm regards,
Sachin
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