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

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Message-ID: <20190813060249.GD6670@kroah.com>
Date:   Tue, 13 Aug 2019 08:02:49 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Nick Crews <ncrews@...omium.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

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 :)

> 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?

thanks,

greg k-h