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From:   Benson Leung <bleung@chromium.org>
Date:   Thu, 1 Dec 2022 13:00:35 -0800
Message-ID: <CANLzEksD=dKgPuCUD74b3YQKCApbZKO_t7Q=tyNKONvAOQ89hw@mail.gmail.com>
Subject: Re: [PATCH] platform/chrome: Create new USB driver for RGB keyboard
 in ChromeOS devices
To:     Prashant Malani <pmalani@chromium.org>
Cc:     Won Chung <wonchung@google.com>, linux-kernel@vger.kernel.org,
        chrome-platform@lists.linux.dev
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Hi Prashant,


On Thu, Dec 1, 2022 at 12:10 PM Prashant Malani <pmalani@chromium.org> wrote:
>
> Hi Won,
>
> On Wed, Nov 30, 2022 at 3:19 PM Won Chung <wonchung@google.com> wrote:
> >
> > Without any driver bound to RGB keyboard, it may not be suspended
> > properly, preventing USB xHCI to be suspended and causing power drain.
> > Create new USB driver for RGB keyboard so that it can be suspended
> > properly.
>
> This seems like overkill. Can't you set this from USB's sysfs nodes
> like power/control [1] ?
>
> [1] https://www.kernel.org/doc/html/latest/driver-api/usb/power-management.html#the-user-interface-for-dynamic-pm
>
>
> Best regards,
>
> -Prashant

We're seeing some behavior where a bound driver is needed in order for
this USB device to properly enter suspend state. Just manipulating the
power/control and other sysfs nodes for this usb device when there's
no driver in the kernel doesn't seem to affect the device's ability to
drop into a usb low power state.

Also, I synced with Won about this offline, but the primary concern is
not this prism usb device runtime suspending, it's actually it's
ability to enter suspend state during system suspend. Right now, this
internal usb device is keeping the whole system from entering lower
S0iX states because it's not sleeping. This driver patch doesn't
address that yet, but I'd like Won to dig down and see if he can get
it suspending at suspend time too.


-- 
Benson Leung
Staff Software Engineer
Chrome OS Kernel
Google Inc.
bleung@google.com
Chromium OS Project
bleung@chromium.org