linux-kernel - Re: Policy to keep USB ports powered in low-power states

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Message-ID: <CAHX4x87DbJ4cKuwVO3OS=UzwtwSucFCV073W8bYHOPHW8NiA=A@mail.gmail.com>
Date:   Wed, 14 Aug 2019 14:12:07 -0600
From:   Nick Crews <ncrews@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Daniel Kurtz <djkurtz@...gle.com>
Subject: Re: Policy to keep USB ports powered in low-power states

Thanks for the fast response!

On Tue, Aug 13, 2019 at 12:02 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Aug 12, 2019 at 06:08:43PM -0600, Nick Crews wrote:
> > Hi Greg!
>
> Hi!
>
> First off, please fix your email client to not send html so that vger
> does not reject your messages :)

Thanks, should be good now.

>
> > I am working on a Chrome OS device that supports a policy called "USB Power
> > Share," which allows users to turn the laptop into a charge pack for their
> > phone. When the policy is enabled, power will be supplied to the USB ports
> > even when the system is in low power states such as S3 and S5. When
> > disabled, then no power will be supplied in S3 and S5. I wrote a driver
> > <https://lore.kernel.org/patchwork/patch/1062995/> for this already as part
> > of drivers/platform/chrome/, but Enric Balletbo i Serra, the maintainer,
> > had the reasonable suggestion of trying to move this into the USB subsystem.
>
> Correct suggestion.
>
> > Has anything like this been done before? Do you have any preliminary
> > thoughts on this before I start writing code? A few things that I haven't
> > figured out yet:
> > - How to make this feature only available on certain devices. Using device
> > tree? Kconfig? Making a separate driver just for this device that plugs
> > into the USB core?
> > - The feature is only supported on some USB ports, so we need a way of
> > filtering on a per-port basis.
>
> Look at the drivers/usb/typec/ code, I think that should do everything
> you need here as this is a typec standard functionality, right?

Unfortunately this is for USB 2.0 ports, so it's not type-C.
Is the type-C code still worth looking at?

>
> thanks,
>
> greg k-h