fix HCD PHY suspend handling

Hi Greg,

Quoted 80 lines · Greg KH

Quoted 79 lines · Roger Quadros

Greg,

Quoted 76 lines · 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.

this should be applied on top of [3] "usb: core: phy: fix return value of usb_phy_roothub_exit()" (even though there's no strict dependency, this is the order I wrote the patches in).

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

Quoted 8 lines

Quoted 5 lines

Quoted 3 lines

Martin Blumenstingl (2):
usb: core: split usb_phy_roothub_{init,alloc}
usb: core: use phy_exit during suspend if wake up is not supported

Gentle ping on this one. Without this system suspend/resume is broken on TI platforms.

Sorry, this missed my merge window, I can pick it up after 4.17-rc1 is out.

do you want me to re-send this based on v4.17-rc1 (once it's out)? I can re-spin this series so it includes:
a) "usb: core: phy: fix return value of usb_phy_roothub_exit()" [0]
b) the two patches from this series (they apply on top of [0])
c) a missing forward declaration as well as a missing include guard (and a SPDX-License-Identifier) as suggested by Masahiro Yamada in [1]

(patches for c) are neither written nor posted yet, but they're minor and I can prepare and test them during the weekend)

just let me know whether you would like to take these three series individually or whether you would like them all in one "usb: core:
phy: fixes for v4.17" series