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Subject: Re: [PATCH v3] usb: dwc3: Add support for VBUS power control
To:     Mark Brown <broonie@kernel.org>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>
CC:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        balbi@kernel.org, gregkh@linuxfoundation.org, lgirdwood@gmail.com
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From:   Mike Looijmans <mike.looijmans@topic.nl>
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On 23-07-2020 13:05, Mark Brown wrote:
> On Thu, Jul 23, 2020 at 09:56:14AM +0200, Vincent Whitchurch wrote:
>> On Fri, Jun 19, 2020 at 04:25:12PM +0200, Mike Looijmans wrote:
>>> +void dwc3_set_vbus(struct dwc3 *dwc, bool enable)
>>> +{
>>> +	int ret;
>>> +
>>> +	if (enable !=3D dwc->vbus_reg_enabled) {
>>> +		if (enable)
>>> +			ret =3D regulator_enable(dwc->vbus_reg);
>>> +		else
>>> +			ret =3D regulator_disable(dwc->vbus_reg);
>  =20
>> dwc->vbus_reg is set to NULL when the regulator is not present.  These
>> regulator_* functions expect a non-NULL pointer so a NULL check is
>> required before calling them.
> Does the device actually support running without power so that's a thing
> that can happen?  _get_optional() should only ever be used for supplies
> that may be physically absent.

It's the 5V VBUS power for the USB "plug" that's being controlled here.=20
It must turned on when the controller is in "host" mode. Some boards=20
arrange this in hardware through the PHY, and some just don't have any=20
control at all and have it permanently on or off. On a board where the=20
5V is controlled using a GPIO line or an I2C chip, this patch is=20
required to make it work.


--=20
Mike Looijmans