[PATCH v1 0/8] phy: qcom-ufs: Enable regulators to be off in suspend

[Evan Green]

The goal with this series is to enable shutting off regulators that power
UFS during system suspend.

In "the good life" version of this, we'd just disable the regulators
in phy_poweroff and be done with it. Unfortunately, that's not symmetric,
as regulators are not enabled during phy_poweron. Ok, so you might think
we could just move the regulator enable and anything else that needs to
come along into phy_poweron, so that we can then undo it all in
phy_poweroff. That's where things get tricky.

The qcom-qmp-phy overloaded the phy_init and phy_poweron callbacks,
basically to mean "init phase 1" and "init phase 2". There are two phases
because they have this phy_reset bit outside of the phy (in the UFS
controller registers), and they need to make sure this bit is toggled at
specific points in the phy init sequence. So there's this implicit
sequence in the init dance between ufs-qcom.c and phy-qcom-qmp.c:
1) ufs-qcom asserts the PHY reset bit.
2) phy-qcom-qmp phy_init does most of its initialization, but exits early.
3) ufs-qcom deasserts the PHY reset bit.
4) phy-qcom-qmp phy_poweron finishes its initialization.

This init dance is very difficult to follow in the code (since it's split
between two drivers and not spelled out well), and arguably represents a
deficiency in the hardware description of these devices.

In this series I'm proposing tweaking the bindings for the Qualcomm
UFS controller and PHY. In it we expose a reset controller from the
UFS controller, that is then picked up and used from the PHY code.
With this, the phy code can be reorganized to complete its initialization
in a single function, removing the implicit two-phase overloading.

Then I can move most of the phy initialization, including enabling
the regulators, into phy_poweron. Now, when phy_poweroff is called,
the phy actually powers off. This finally disables the regulators
and allows me to save power in system suspend.

Because the UFS PHY reset bit is now toggled in the PHY, rather
than in ufs-qcom, this also percolated to all other PHYs using
ufs-qcom, which from what I can see is just 8996.

There are a couple of tradeoffs in this series that I'd welcome feedback
on. First, it breaks compatibility with device trees that don't expose
this new reset controller. Making this work with older device trees
would be pretty ugly in the code, and given that the SDM845 UFS DT nodes
aren't accepted upstream yet, the breakage seemed worth it. I'm not as
sure about 8996.

Second, I removed the calls to phy_poweroff during clock gating. This
was originally dialing down a clock or two, while leaving the phy powered.
I've now changed the semantics of phy_poweroff to, well, actually power off.
This works great for userlands that have set UFS's spm_lvl to 5 (off) like
I have, but maybe changes power consumption for devices that have spm_lvl
set to 3. I could try to use phy_init and phy_poweron as the two different
possible transitions (fully off, and clocks off respectively), but I'm not
sure if it actually matters, and I like the idea that phy_poweroff really
does power the thing off.

Also, I don't have an 8996 device to test. If someone is able to test this
out and perhaps point out any (hopefully obvious) bugs in the 8996 portion,
I'd be grateful.

This patch is based atop phy-next, plus the UFS DT nodes, which are now
patch 3, 4, 5 of [1].

[1] https://lore.kernel.org/lkml/20181210192826.241350-1-evgreen@xxxxxxxxxxxx/


Evan Green (8):
  dt-bindings: phy-qcom-qmp: Add UFS PHY reset
  dt-bindings: phy: qcom-ufs: Add resets property
  arm64: dts: sdm845: Add UFS PHY reset
  arm64: dts: msm8996: Add UFS PHY reset controller
  scsi: ufs: qcom: Expose the reset controller for PHY
  phy: qcom-qmp: Utilize UFS reset controller
  phy: qcom-qmp: Move UFS phy to phy_poweron/off
  phy: qcom-ufs: Refactor all init steps into phy_poweron

 .../devicetree/bindings/phy/qcom-qmp-phy.txt  |   6 +-
 .../devicetree/bindings/ufs/ufs-qcom.txt      |   1 +
 arch/arm64/boot/dts/qcom/msm8996.dtsi         |   4 +-
 arch/arm64/boot/dts/qcom/sdm845.dtsi          |   3 +
 drivers/phy/qualcomm/phy-qcom-qmp.c           | 123 ++++++++++--------
 drivers/phy/qualcomm/phy-qcom-ufs-i.h         |   5 +-
 drivers/phy/qualcomm/phy-qcom-ufs-qmp-14nm.c  |  25 +---
 drivers/phy/qualcomm/phy-qcom-ufs-qmp-20nm.c  |  25 +---
 drivers/phy/qualcomm/phy-qcom-ufs.c           |  57 ++++++--
 drivers/scsi/ufs/Kconfig                      |   1 +
 drivers/scsi/ufs/ufs-qcom.c                   | 110 +++++++++-------
 drivers/scsi/ufs/ufs-qcom.h                   |   4 +
 12 files changed, 197 insertions(+), 167 deletions(-)

-- 
2.18.1