[PATCH usb v6 0/6] usb/core/phy fixes for v4.17

[Martin Blumenstingl]

This is a follow-up to my previous series "initialize (multiple) PHYs
for a HCD": [0].

Roger Quadros reported [1] that it "is breaking low power cases on TI
SoCs when USB is in host mode". He further explains that "Not doing the
phy_exit() here [when entering suspend] leaves the clocks enabled on
our SoC and we're no longer able to reach low power states on system
suspend."
Chunfeng Yun from Mediatek noted [2] that we cannot unconditionally call
phy_exit while entering system suspend, because this would "disconnect
plugged devices on MTK platforms, due to re-initialize u2 phys when
resume"

In the discussion (which followed Roger's bug report: [1]) Roger,
Chunfeng and me came to the conclusion that we can fix suspend on the
TI SoCs without breaking it on the Mediatek SoCs by extending the
suspend and resume code in usb/core/phy.c by checking whether the USB
controller can wake up the system (which is the case for the Mediatek
MTU3 controller, but now for the dwc3 controller used on the TI SoCs):
- if the controller can wake up the system (Mediatek MTU3 use-case) we
  only call usb_phy_roothub_power_off (which calls phy_power_off) when
  entering system suspend
- if the controller however cannot wake up the system (dwc3 on TI SoCs)
  we additionally call usb_phy_roothub_exit (which calls phy_exit) when
  entering system suspend
- (we undo the previous steps during system resume)

The goal of this series is to fix the issue reported by Roger without
breaking suspend/resume on the Mediatek SoCs.
Since I neither have a TI nor a Mediatek device I am sending this as
RFC. I have tested it on an Amlogic Meson GXM board (Khadas VIM2) which
does NOT support suspend/resume yet.

Additionally Stefan Wahren reported [7] that booting on a Raspberry Pi
with CONFIG_GENERIC_PHY being disabled (which is the case for
bcm2835_defconfig) breaks USB. A fix for this is also included.


changes since v5 at [9]
- rebased on top of v4.17-rc1
- added Keerthy's Tested-by to the first three patches (thank you!)
- fixed a checkpatch warning (which was introduced in v4.17-rc1's
  checkpatch.pl) in patch #6 by using "/* SPDX-License-Identifier"
  instead of "// SPDX-License-Identifier"

changes since v4 at [8]
- updated series title since it now includes fixes for other
  functionality than suspend
- rebased on top of f8cf2f16a7c95a from Linus' tree -> I will re-send
  an updated version once v4.17-rc1 is out, I just sent it early to
  get some feedback early!
- included patch [3] "usb: core: phy: fix return value of
  usb_phy_roothub_exit()" in this series
- fix the logic if CONFIG_GENERIC_PHY is disabled (as reported by
  Stefan Wahren, new patch #4)
- two minor coding style fixes as suggested by Masahiro Yamada (new
  patches #4 and #5)

changes since RFC v3 at [6]:
- added Chunfeng Yun's Tested-by and Roger Quadros' Reviewed-by (thank
  you!)
- dropped RFC prefix

changes since RFC v2 at [5]:
- add missing INIT_LIST_HEAD call in usb_phy_roothub_add_phy (affects
  patch #1 - spotted by Roger Quadros, thank you!)
- fixed swapped conditions using device_may_wakeup() in
  usb_phy_roothub_resume because we need to call usb_phy_roothub_init
  if the controller cannot wake up the device (affects patch #2, spotted
  by Chunfeng Yun, thank you!)
- simplified the error condition to "undo" usb_phy_roothub_init if
  usb_phy_roothub_power_on failed in usb_phy_roothub_resume (suggested
  by Chunfeng Yun)
- updated the commit message (using Roger's wording) because (quote from
  Roger "it doesn't prevent the system from entering suspend but just
  prevents the system from reaching lowest power levels in the suspend
  state."

Changes since RFC v1 (blob attachments) at [4]:
- use device_may_wakeup instead of device_can_wakeup as suggested by
  Roger Quadros
- use the controller device from hcd->self.controller as suggested by
  Chunfeng Yun
- compile time fixes thanks to Roger Quadros
- if usb_phy_roothub_power_on in usb_phy_roothub_resume failes then
  we now call usb_phy_roothub_exit to keep the PHYs in the correct
  state if usb_phy_roothub_resume partially failed


[0] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006599.html
[1] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006737.html
[2] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006758.html
[3] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006819.html
[4] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006794.html
[5] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006820.html
[6] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006847.html
[7] https://www.spinics.net/lists/linux-usb/msg167472.html
[8] http://lists.infradead.org/pipermail/linux-amlogic/2018-March/006882.html
[9] http://lists.infradead.org/pipermail/linux-amlogic/2018-April/007009.html

Martin Blumenstingl (6):
  usb: core: phy: fix return value of usb_phy_roothub_exit()
  usb: core: split usb_phy_roothub_{init,alloc}
  usb: core: use phy_exit during suspend if wake up is not supported
  usb: core: phy: make it a no-op if CONFIG_GENERIC_PHY is disabled
  usb: core: phy: add missing forward declaration for "struct device"
  usb: core: phy: add the SPDX-License-Identifier and include guard

 drivers/usb/core/hcd.c | 18 +++++---
 drivers/usb/core/phy.c | 93 ++++++++++++++++++++++++++++++------------
 drivers/usb/core/phy.h | 22 +++++++++-
 3 files changed, 99 insertions(+), 34 deletions(-)

-- 
2.17.0