linux-kernel - Re: [PATCH RFC] usb: dwc2: power off during shutdown

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Message-ID: <470783016.30183.1536172949193@email.1und1.de>
Date:   Wed, 5 Sep 2018 20:42:29 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, Doug Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] usb: dwc2: power off during shutdown

Hi Minas,

> Minas Harutyunyan <Minas.Harutyunyan@...opsys.com> hat am 5. September 2018 um 10:37 geschrieben:
> 
> 
> Hi Stefan,
> 
> On 9/1/2018 1:55 PM, Stefan Wahren wrote:
> > Currently USB consumes a lot of power after shutting down a Raspberry Pi 3
> > (example setup with Ethernet and a keyboard connected). So power off
> > USB on shutdown.
> > 
> > Measured on Raspberry Pi 3B with 4.19rc1/multi_v7_defconfig (HDMI, Ethernet
> > and a keyboard connected)
> > 
> > Before patch: 2.450 W
> > After patch:  2.090 W
> > 
> 
> Could you please elaborate. Power measurements done after shutdown?

I did the following:

sudo halt
wait until "System halted" appears on the screen
"measured" the current value displayed on my PSU

You are right that not the same as poweroff. But in even in poweroff the board consumes 0.6 W, but in this case USB is powered down.

> Why 
> your setup continue consume power after shutdown?

The BCM2835 SoC has a GPU and a ARM core. Linux is running only on the ARM core. The GPU is usually running a close source firmware, which is started at first during boot und runs all the time.

> Maybe its 
> sleep/hibernation mode?

There isn't much implementation of power management for BCM2835 yet. So i wanted to start with USB.
Even for sleep/hibernation the consumption is much too high. Because the system consumes in idle 1.6 W.

> 
> dwc2 core in your platform which type of power optimization supports: 
> partial power down, hibernation or extended hibernation? Please provide 
> me GHWCFG4 register value of your core.

AFAIK all RPis use the same USB IP core:

GHWCFG4 = 0x1ff00020

Stefan