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

[Doug Anderson]

Kishon,

On Mon, Jun 3, 2019 at 8:22 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> Kishon,
>
> On Mon, Jun 3, 2019 at 4:22 AM Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> >
> > Hi,
> >
> > On 20/05/19 1:34 PM, Caesar Wang wrote:
> > > Hi Doug,
> > >
> > > For now,  nobody of rockchip is responsible for this driver.
> > > Cc: Nickey, Zain, Hjc
> > >
> > >
> > > On 5/8/19 7:48 AM, Douglas Anderson 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@xxxxxxxxxxxx>
> > >
> > >
> > > Reviewed-by: Caesar Wang <wxt@xxxxxxxxxxxxxx>
> > >
> > >> ---
> > >> 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(-)
> > >>
> > >> diff --git a/drivers/phy/rockchip/phy-rockchip-dp.c
> > >> b/drivers/phy/rockchip/phy-rockchip-dp.c
> > >> index 8b267a746576..10bbcd69d6f5 100644
> > >> --- a/drivers/phy/rockchip/phy-rockchip-dp.c
> > >> +++ b/drivers/phy/rockchip/phy-rockchip-dp.c
> > >> @@ -35,7 +35,7 @@ struct rockchip_dp_phy {
> > >>   static int rockchip_set_phy_state(struct phy *phy, bool enable)
> > >>   {
> > >>       struct rockchip_dp_phy *dp = phy_get_drvdata(phy);
> > >> -    int ret;
> > >> +    int ret = 0;
> > >>         if (enable) {
> > >>           ret = regmap_write(dp->grf, GRF_SOC_CON12,
> > >> @@ -50,9 +50,12 @@ static int rockchip_set_phy_state(struct phy *phy, bool
> > >> enable)
> > >>       } else {
> > >>           clk_disable_unprepare(dp->phy_24m);
> > >>   -        ret = regmap_write(dp->grf, GRF_SOC_CON12,
> > >> -                   GRF_EDP_PHY_SIDDQ_HIWORD_MASK |
> > >> -                   GRF_EDP_PHY_SIDDQ_OFF);
> > >> +        /*
> > >> +         * Intentionally don't turn SIDDQ off when disabling
> > >> +         * the PHY.  There is a power leak on rk3288 and
> > >> +         * suspend power _increases_ by 5 mA if you turn this
> > >> +         * off.
> > >> +         */
> >
> > Can someone in Rockchip try to find the root-cause of the issue? Keeping the
> > PHY off shouldn't increase power draw.
>
> It sounded like Caesar already answered this, though?  Basically things
> aren't hooked up in a way that this line can be turned safely turned
> off in rk3288 with the current state of the world.  Chris says that
> there's an ordering problem where we've got to turn off PD_VIO
> _before_ we turn off SIDDQ.  ...but PD_VIO is a power domain that
> contains much more than just eDP.  So if we truly wanted to try to
> solve this we'd need to come up with a way to make sure PD_VIO got all
> the way off and then turn this off only afterwards.
>
> ...and right now on rk3288 it looks like we never actually turn off
> PD_VIO while the system is running.

Is now a good time to land this patch since 5.3-rc1 is out?  Do you
need me to re-send?  Hopefully your concerns are all addressed?

-Doug