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

[Kishon Vijay Abraham I]

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
>> ÂÂÂ other way we can revert this patch.
>> B) If someone can show that their particular board doesn't have this
>> ÂÂÂ power leak (maybe they have rails hooked up differently?) we can
>> ÂÂÂ 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
>> ÂÂÂ 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.
>>
>> Â drivers/phy/rockchip/phy-rockchip-dp.c | 11 +++++++----
>> Â 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 {
>> Â static int rockchip_set_phy_state(struct phy *phy, bool enable)
>> Â {
>> ÂÂÂÂÂ struct rockchip_dp_phy *dp = phy_get_drvdata(phy);
>> -ÂÂÂ int ret;
>> +ÂÂÂ int ret = 0;
>> Â ÂÂÂÂÂ if (enable) {
>> ÂÂÂÂÂÂÂÂÂ ret = regmap_write(dp->grf, GRF_SOC_CON12,
>> @@ -50,9 +50,12 @@ static int rockchip_set_phy_state(struct phy *phy, bool
>> enable)
>> ÂÂÂÂÂ } else {
>> ÂÂÂÂÂÂÂÂÂ clk_disable_unprepare(dp->phy_24m);
>> Â -ÂÂÂÂÂÂÂ ret = regmap_write(dp->grf, GRF_SOC_CON12,
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ GRF_EDP_PHY_SIDDQ_HIWORD_MASK |
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ GRF_EDP_PHY_SIDDQ_OFF);
>> +ÂÂÂÂÂÂÂ /*
>> +ÂÂÂÂÂÂÂÂ * Intentionally don't turn SIDDQ off when disabling
>> + * the PHY. There is a power leak on rk3288 and
>> +ÂÂÂÂÂÂÂÂ * suspend power _increases_ by 5 mA if you turn this
>> +ÂÂÂÂÂÂÂÂ * off.
>> +ÂÂÂÂÂÂÂÂ */

Can someone in Rockchip try to find the root-cause of the issue? Keeping the
PHY off shouldn't increase power draw.

Thanks
Kishon