linux-kernel - Re: [PATCH] phy: rockchip-dp: Avoid power leak by leaving the PHY power on

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Date:   Sat, 18 May 2019 09:51:06 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Doug Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Kishon Vijay Abraham I <kishon@...com>
Cc:     Elaine Zhang <zhangqing@...k-chips.com>,
        Caesar <wxt@...k-chips.com>, Lin Huang <hl@...k-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Derek Basehore <dbasehore@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Ryan Case <ryandcase@...omium.org>
Subject: Re: [PATCH] phy: rockchip-dp: Avoid power leak by leaving the PHY power on

Hi,

Am Samstag, 18. Mai 2019, 01:57:47 CEST schrieb Doug Anderson:
> Elaine and Caesar,
> 
> On Tue, May 7, 2019 at 4:50 PM Douglas Anderson <dianders@...omium.org> wrote:
> >
> > While testing a newer kernel on rk3288-based Chromebooks I found that
> > the power draw in suspend was higher on newer kernels compared to the
> > downstream Chrome OS 3.14 kernel.  Specifically the power of an
> > rk3288-veyron-jerry board that I tested (as measured by the smart
> > battery) was ~16 mA on Chrome OS 3.14 and ~21 mA on a newer kernel.
> >
> > I tracked the regression down to the fact that the "DP PHY" driver
> > didn't exist in our downstream 3.14.  We relied on the eDP driver to
> > turn on the clock and relied on the fact that the power for the PHY
> > was default turned on.
> >
> > Specifically the thing that caused the power regression was turning
> > the eDP PHY _off_.  Presumably there is some sort of power leak in the
> > system and when we turn the PHY off something is leaching power from
> > something else and causing excessive power draw.
> >
> > Doing a search through device trees shows that this PHY is only ever
> > used on rk3288.  Presumably this power leak is present on all
> > rk3288-SoCs running upstream Linux so let's just whack the driver to
> > make sure we never turn off power.  We'll still leave the parts that
> > turn _on_ the power and grab the clock, though.
> >
> > NOTES:
> > A) If someone can identify what this power leak is and fix it in some
> >    other way we can revert this patch.
> > B) If someone can show that their particular board doesn't have this
> >    power leak (maybe they have rails hooked up differently?) we can
> >    perhaps add a device tree property indicating that for some boards
> >    it's OK to turn this rail off.  I don't want to add this property
> >    until I know of a board that needs it.
> >
> > Fixes: fd968973de95 ("phy: Add driver for rockchip Display Port PHY")
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> > As far as I know Yakir (the original author) is no longer at Rockchip.
> > I've added a few other Rockchip people and hopefully one of them can
> > help direct even if they're not directly responsible.
> >
> >  drivers/phy/rockchip/phy-rockchip-dp.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> Can you help direct this to the right person?  ...or should we just
> land it and assume it's fine?

I tink Kishon as phy-maintainer is the correct person to take on this
patch, but maybe he's waiting for the merge-window to be over.


Heiko