Re: [PATCH v3] usb: dwc3: Add support for VBUS power control

From: Mike Looijmans
Date: Mon Jul 27 2020 - 07:50:37 EST

Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert

TOPIC Embedded Products B.V.
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On 27-07-2020 12:23, Mark Brown wrote:
On Sun, Jul 26, 2020 at 09:10:39AM +0200, Mike Looijmans wrote:
On 23-07-2020 13:05, Mark Brown wrote:

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

That sounds like the driver should not be using _get_optional() then.

Making it mandatory would break most (read: all except Topic's) existing boards as they won't have it in their devicetree. I'm perfectly okay with that, but others might disagree.