Hi

On 5/21/21 4:26 PM, Heiner Kallweit wrote:

On 21.05.2021 10:19, Heiner Kallweit wrote:

quoted

Before the referenced commit we used i801_suspend and i801_resume also as
runtime pm callbacks. That's no longer the case, and at least on my
platform the SMBus controller PCI device doesn't support PM. Therefore
PCI core can't do what it would do for other devices: bring them to D3hot
or D3cold.
Having said that effectively there is no runtime pm any longer. Not sure
whether there are SMBus controller versions where the PCI device supports
PM.

About commit a9c8088c7988 which removes the runtime PM callbacks: It 
indeed had a runtime PM regression but is fixed by commit c5eb1190074c 
("PCI / PM: Allow runtime PM without callback functions").

quoted

So my questions are:
Does the SMBus controller support any power-saving modes?
i801_suspend() just sets SMBHSTCFG to the value it had when the driver
was loaded. Means if SMBHSTCFG_HST_EN was enabled already, we won't clear
it. And this bit may have an impact on some internal PLL's (just guessing).
If there's no good-enough power-saving option, then runtime pm support
could be removed completely, or?


00:1f.4 SMBus: Intel Corporation Cannon Lake PCH SMBus Controller (rev 10)
         DeviceName: Onboard - Other
         Subsystem: ASUSTeK Computer Inc. Device 8694
         Flags: medium devsel, IRQ 16
         Memory at a1316000 (64-bit, non-prefetchable) [size=256]
         I/O ports at efa0 [size=32]
         Kernel driver in use: i801_smbus
         Kernel modules: i2c_i801

It's not entirely clear to me either is it HW or FW specific what 
platform supports PCI PM for the SMBus controller. But usually what I've 
seen Core based platforms don't have it while *some* Atom based does have.

I saw your message earlier today and was looking at from our lab 
machines which have it. I'm quite sure but not absolutely one Apollo 
Lake one had it but today didn't see it. Need to check with colleagues 
did they change BIOS etc. Or I just remember wrong :-)

Fortunately one Braswell based have the PM. Here's the lspic output from 
kernel 5.13.0-rc2:

# lspci -s 00:1f.3 -vv
00:1f.3 SMBus: Intel Corporation Atom/Celeron/Pentium Processor 
x5-E8000/J3xxx/N3xxx SMBus Controller (rev 31)
     Subsystem: Intel Corporation Atom/Celeron/Pentium Processor 
x5-E8000/J3xxx/N3xxx SMBus Controller
     Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR- FastB2B- DisINTx-
     Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
     Interrupt: pin B routed to IRQ 18
     Region 0: Memory at 9191c000 (32-bit, non-prefetchable) [size=32]
     Region 4: I/O ports at 2040 [size=32]
     Capabilities: [50] Power Management version 3
         Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA 
PME(D0-,D1-,D2-,D3hot-,D3cold-)
         Status: D3 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
     Kernel driver in use: i801_smbus
     Kernel modules: i2c_i801

So the PCI device needs to have Power Management capability and here the 
current status is SMBus controller is suspended to D3 state.

Jarkko