On Wed, Apr 27, 2016 at 06:25:16PM +0800, Jisheng Zhang wrote:
> On Wed, 27 Apr 2016 10:57:39 +0100 Mark Brown wrote:
> > On Wed, Apr 27, 2016 at 08:37:20AM +0300, Felipe Balbi wrote:

> > > > +	vbus = devm_regulator_get(&pdev->dev, "vbus");  

> > > devm_regulator_get_optional() ??  

> > Does USB work without a VBUS?  Unless the answer is yes then I'd expect
> > this to be just a normal regulator_get().

> Per spec no. But the vbus may be transparent to SW on some platforms, so I
> think devm_regulator_get_optional() is better.

Really, no.  If it's physically there the software needs to be written
as such.  Please see the documentation and list archives for extensive
discussion on this topic.

> > This is all completely broken unless the supply is optional.

> The supply is optional.

To repeat a supply is only optional if it might be physically absent.