linux-kernel - Re: [PATCH v2 1/3] dt-bindings: usb: ci-hdrc-usb2: add property disable-runtime-pm

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Date:   Fri, 17 Jul 2020 08:14:58 -0600
From:   Rob Herring <robh@...nel.org>
To:     Peter Chen <peter.chen@....com>
Cc:     Philippe Schenker <philippe.schenker@...adex.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] dt-bindings: usb: ci-hdrc-usb2: add property disable-runtime-pm

On Thu, Jul 16, 2020 at 8:31 PM Peter Chen <peter.chen@....com> wrote:
>
> On 20-07-16 13:24:52, Rob Herring wrote:
> > On Tue, Jul 14, 2020 at 05:18:20PM +0200, Philippe Schenker wrote:
> > > Chipidea depends on some hardware signals to be there in order
> > > for runtime-pm to work well. Add the possibility to disable runtime
> > > power management that is necessary for certain boards.
> >
> > This is why we have SoC specific compatible strings. Use that.
>
> It is a board design limitation, not SoC's. To support USB low power
> mode for device mode, either VBUS connects to SoC, or VBUS connect to
> GPIO, or VBUS connect to Type-C IC, but none of the design is used
> at that board. So the USB can't enter low power mode for that board,
> otherwise, the USB controller can't be woken up since no any interrupts
> will occur if USB cable (host at other side) connects to the connector.

That's certainly a better explanation than the original.

Don't you need to describe the Vbus connection in the above cases?
Then you could handle this case based on the lack of a Vbus
description?

Rob