linux-kernel - Re: [PATCH can-next v4] can: add tx/rx LED trigger support

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Message-ID: <50191509.8030404@pengutronix.de>
Date:	Wed, 01 Aug 2012 13:37:45 +0200
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Fabio Baltieri <fabio.baltieri@...il.com>
CC:	linux-can@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>
Subject: Re: [PATCH can-next v4] can: add tx/rx LED trigger support

On 08/01/2012 12:30 PM, Fabio Baltieri wrote:
[...]
>>> +void can_led_init(struct net_device *netdev)
>>> +{
>>> +	struct can_priv *priv = netdev_priv(netdev);
>>> +	void *res;
>>> +
>>> +	res = devres_alloc(can_led_release, 0, GFP_KERNEL);
>>                                             ^
>> I'm not really sure if this is working. For example, pinctrl [1]
>> allocates a double pointer here. The res pointer here and in
>> can_led_release simply points to invalid memory. But as long as you
>> don't dereference it, it should work.
>>
>> [1] http://lxr.free-electrons.com/source/drivers/pinctrl/core.c#L862
> 
> Actually that's also used by libata-core (not in lxr yet) and dma-mapping:
> 
> http://lxr.free-electrons.com/source/drivers/base/dma-mapping.c#L193
> 
> actually, res should point at the end of some internal devres structure,
> and is only used as return value in this case.
> 
> Of course, in this case the release function can only use the struct
> device pointer.
> 
> I've run some fail test and ftraced the whole thing and it seems to work
> pretty good!  I'll send a v5 with the rename later.

Thanks for checking. I just noticed, the pinctrl usecase is a bit different.

Marc
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