linux-kernel - Re: [PATCH v3] usb: dwc2: dwc2_vbus_supply

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Date:   Thu, 22 Mar 2018 14:34:10 +0100
From:   Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     linux-kernel@...r.kernel.org,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Amelie Delaunay <amelie.delaunay@...com>,
        Minas Harutyunyan <hminas@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v3] usb: dwc2: dwc2_vbus_supply_init: fix error check

On 03/22/2018 02:26 PM, Heiko Stübner wrote:
> Am Donnerstag, 22. März 2018, 14:14:51 CET schrieb Tomeu Vizoso:
>> devm_regulator_get_optional returns -ENODEV if the regulator isn't
>> there, so if that's the case we have to make sure not to leave -ENODEV
>> in the regulator pointer.
>>
>> Also, make sure we return 0 in that case, but correctly propagate any
>> other errors. Also propagate the error from _dwc2_hcd_start.
>>
>> Fixes: 531ef5ebea96 ("usb: dwc2: add support for host mode external vbus
>> supply") Cc: Amelie Delaunay <amelie.delaunay@...com>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>>
>> ---
>>
>> v2: Only overwrite the error in the pointer after checking it (Heiko
>>      Stübner <heiko@...ech.de>)
>> v3: Remove hunks that shouldn't be in this patch
>> ---
>>   drivers/usb/dwc2/hcd.c | 11 +++++++----
>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index dcfda5eb4cac..863aed20517f 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -359,8 +359,13 @@ static void dwc2_gusbcfg_init(struct dwc2_hsotg *hsotg)
>> static int dwc2_vbus_supply_init(struct dwc2_hsotg *hsotg)
>>   {
>>   	hsotg->vbus_supply = devm_regulator_get_optional(hsotg->dev, "vbus");
>> -	if (IS_ERR(hsotg->vbus_supply))
>> +	if (PTR_ERR(hsotg->vbus_supply) == -ENODEV) {
>> +		hsotg->vbus_supply = NULL;
>>   		return 0;
>> +	} else if (IS_ERR(hsotg->vbus_supply)) {
>> +		hsotg->vbus_supply = NULL;
>> +		return PTR_ERR(hsotg->vbus_supply);
>> +	}
> 
> my personal cluelessnes, but can you use PTR_ERR without checking for
> IS_ERR first?

It's just a cast, so it should be fine.

> I would've expected something along the line of
> 
> if (IS_ERR(hsotg->vbus_supply)) {
> 	if (PTR_ERR(hsotg->vbus_supply) == -ENODEV) {
> 		hsotg->vbus_supply = NULL;
> 		return 0;
> 	} else {
> 		return PTR_ERR(hsotg->vbus_supply);
> 	}
> }

I kind of liked to avoid one indentation level. Also wanted to play safe 
and NULLify the pointer in both code paths.

Thanks,

Tomeu