linux-kernel - Re: [PATCH] usb: phy: generic: request regulator optionally

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Date:   Wed, 7 Sep 2016 10:25:47 +0300
From:   Roger Quadros <rogerq@...com>
To:     Stefan Agner <stefan@...er.ch>, Mark Brown <broonie@...nel.org>
CC:     Felipe Balbi <balbi@...nel.org>, <gregkh@...uxfoundation.org>,
        <fabio.estevam@....com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: phy: generic: request regulator optionally

Hi Stefan,

On 06/09/16 21:01, Stefan Agner wrote:
> On 2016-09-06 01:22, Mark Brown wrote:
>> On Tue, Sep 06, 2016 at 10:45:19AM +0300, Felipe Balbi wrote:
>>> Stefan Agner <stefan@...er.ch> writes:
>>
>>>> According to the device tree bindings the vcc-supply is optional.
>>
>> This is nonsense unless the device can work without this supply.  Given
>> that the supply is called VCC that doesn't seem entirely likely.
> 
> Afaik it is kind of a generic device tree binding, I guess the physical
> device can have various appearances and properties...
> 
> A quick survey showed several device trees which do not specify
> vcc-supply...
> 
> That said, I checked the device at hand, and it actually has a USB PHY
> power supply inputs, but the device tree does not model them.
> 
>>>> +	nop->vcc = devm_regulator_get_optional(dev, "vcc");
>>>>  	if (IS_ERR(nop->vcc)) {
>>>>  		dev_dbg(dev, "Error getting vcc regulator: %ld\n",
>>>>  					PTR_ERR(nop->vcc));
>>>> -		if (needs_vcc)
>>>> -			return -EPROBE_DEFER;
>>>> +		if (needs_vcc || PTR_ERR(nop->vcc) == -EPROBE_DEFER)
>>>> +			return PTR_ERR(nop->vcc);
>>
>>> does this look okay from a regulator API perspective?
>>
>> That's how to use _get_optional() but it's really unusual that you
>> should be using _get_optional().
> 
> Despite the above findings, I still think it is the right thing to do as
> long as we specify vcc-supply to be optional.
> 

I think the right behaviour would be that if vcc-supply is specified in the
DT then failure to get that supply is a serious failure and probe should fail.

So the correct fix would be to call devm_regulator_get() only if needs_vcc is true.

cheers,
-roger