[Bug 90075] [BYT LPSS backlight] Acer Aspire Switch 10 backlight control

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90075

--- Comment #18 from darlor at seznam.cz ---
Created attachment 134602
  --> https://bugs.freedesktop.org/attachment.cgi?id=134602&action=edit
3 dmesg with different pci kernel parameters

Hello everyone,
I think (hope) I identified underlying problem why PCI device 8086-0F08 PWM
Controller is not detected. (without it backlight will not work)
But now I'm stuck because I`m not familiar with PCI Bus, e820 etc... and to be
honest I don`t exactly know what I`m looking at...

First let me explain my thoughts:

On Windows using SIV - System Information Viewer I can see:

Bus-Numb-Fun IRQ Vendor-Dev-Sub_OEM-Rev Class (0:63) Vendor and Device
Description

0-00-0 8086-0F00-09281025-0F Host Bridge      Intel Atom SSA-CUnit
0-02-0 8086-0F31-09281025-0F VGA Controller   Intel Atom Gen7 [GPU-0]
0-20-0 8086-0F35-09281025-0F XHCI Controller  Intel Atom USB xHCI Host Cntrlr
0-26-0 8086-0F18-09281025-0F Other Encryption Intel Atom SEC
0-30-1 8086-0F08-09281025-0F Other Interface  Intel Atom LPIO1 PWM Controller
0-31-0 8086-0F1C-09281025-0F ISA Bridge       Intel Atom Power Control Unit 0

None of these devices is mentioned in DSDT. (at least by Vendor-Device code)

lspci on linux shows something like:

00:00.0 0600: 8086:0f00 Host bridge: Intel Corporation...
00:02.0 0300: 8086:0f31 VGA compatible controller...
00:14.0 0c03: 8086:0f35 USB controller...
00:1a.0 1080: 8086:0f18 Encryption controller...
00:1f.0 0601: 8086:0f1c ISA bridge...

ACPI-IDs are same, but PWM controller is missing. So I think that PWM
controller is connected to PCI bus. (CONFIG_PWM_LPSS_PCI must be enabled so
pwm-lpss-pci.ko module can be used). But why this PCI device is not detected?
Lets have a look on kernel messages in file 'dmesg_nothing_special'

Lines that caught my eyes:

PCI: MMCONFIG for domain 0000 [bus 00-3f] at [mem 0xe0000000-0xe3ffffff] (base
0xe0000000)
PCI: not using MMCONFIG
PCI: Using configuration type 1 for base access
PCI: MMCONFIG for domain 0000 [bus 00-3f] at [mem 0xe0000000-0xe3ffffff] (base
0xe0000000)
[Firmware Info]: PCI: MMCONFIG at [mem 0xe0000000-0xe3ffffff] not reserved in
ACPI motherboard resources
PCI: not using MMCONFIG
PCI: Using host bridge windows from ACPI; if necessary, use "pci=nocrs" and
report a bug
ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff])
acpi PNP0A08:00: fail to add MMCONFIG information, can't access extended PCI
configuration space under this bridge.
Expanded resource Reserved due to conflict with PCI Bus 0000:00

So I googled a little bit and added kernel parameter "memmap=64M\$0xe0000000"
so the extended PCI configuration space 0x00000000e0000000-0x00000000e3ffffff
is reserved. (don't forget that $ needs to be escaped with '\' or '\\\' in
/etc/default/grub). This dmesg is in file 'dmesg_memmap_64M_0xe0000000'
[https://www.centos.org/forums/viewtopic.php?t=53903]

and I got:

PCI: MMCONFIG for domain 0000 [bus 00-3f] at [mem 0xe0000000-0xe3ffffff] (base
0xe0000000)
PCI: MMCONFIG at [mem 0xe0000000-0xe3ffffff] reserved in E820
PCI: Using configuration type 1 for base access
PCI: Using host bridge windows from ACPI; if necessary, use "pci=nocrs" and
report a bug
ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff])
acpi PNP0A08:00: [Firmware Info]: MMCONFIG for domain 0000 [bus 00-3f] only
partially covers this bridge
Expanded resource Reserved due to conflict with PCI Bus 0000:00

So, MMCONFIG only partially covers extended configuration for this bridge. I
don`t exactly know what it means. Only that made sense was to add pci=nocrs,
but it did not solve a thing except that line:
Expanded resource Reserved due to conflict with PCI Bus 0000:00
is not in dmesg anymore.

This dmesg is in file 'dmesg_memmap_64M_0xe0000000_pci_nocrs'.

Could someone please confirm, that it make sense and/or provide some tips how
to go forward?

Thanks

('cut -d" " -f6-' < dmesg > graphical_diff makes dmesgs very easy to compare
:-) )

-- 
You are receiving this mail because:
You are the assignee for the bug.
You are the QA Contact for the bug.
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20171001/2b9a8f84/attachment.html>