Substitute complicated PNLF _UID implementation

[zhen-zen]

Current SSDT-PNLF relies on PCI and MMIO access from ACPI space. However, only proper _UID is required for most cases. Workarounds like BacklightRegistersFix are also available in WhateverGreen.

By moving _UID identification to WhateverGreen, it's possible to make PNLF device a simple stub matched by AppleIntelPanel. Purposed solution is to use a ACPI method SUID that accepts desired _UID from WhateverGreen. It might need extra work to replace it by patching AppleIntelPanel::start which evaluates _UID.

Sample DSDT attached in the commit but will remove later.

Tested on 8086:9b41 (CML, faked to 3e9b) and 8086:5927 (KBL-R, faked to 5926).

[zhen-zen]

Is it good to just replace it with CPUInfo::CpuGeneration ?

[Lorys89]

it's a great idea and I'm available to test over multiple generations in my hacks.

[Sher1ocks]

is it support snow leopard and lion?

[vit9696]

Thanks!

• Is it reliable? I am worried about data races between updating UID by ourselves and macOS reading it.
• CPU generation feels the right way to do the UID detection to me, but it will need more thorough testing and possibly updates to the CPU detection code.
• What are the downsides of the SSDT route besides the complexity?

[zhen-zen]

is it support snow leopard and lion?

The implementation should be compatible with older OS but currently I don't have such platforms for testing.

Also @Lorys89 mentioned failure on his Haswell laptop. Will discuss it below.

Thanks!

• Is it reliable? I am worried about data races between updating UID by ourselves and macOS reading it.

I put it in processBuiltinProperties() which is called during init(). So it's executed before any Framebuffer and AppleBacklight. Also, all init() happens before AppleIntelPanel::start reads _UID with evaluateInteger.

I don't know how to figure out the class structure in IOKit, here is my best guess:

And before the fix kicks in, ACPI driver will first evaluate every _UID and then publish it in ioreg. That's what the latter cosmetic part does.

• CPU generation feels the right way to do the UID detection to me, but it will need more thorough testing and possibly updates to the CPU detection code.

I agree it's the correct way, but sometimes iGPUs like UHD620 might be wrongly classified. We to find a way out for some corner cases. However I suppose It could be deducted from current list? Or maybe by checking which Framebuffer is loaded?

• What are the downsides of the SSDT route besides the complexity?

The SSDT applies fixes for some early generations. However, the variant targeting CFL does nothing while we also have a fix in WEG. I also doubt if the extra work is needed for SKL+. It's better to keep the fix in a single place for less interference in further debugging.

If only the PWMMAX is required for override, or the HSW case, I suppose we can implement that in WEG since we also has access via readRegister32. Or maybe something like https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/i915/display/intel_panel.c#L835 .

This new feature should do nothing with old SSDT that has no SUID method. We can revert the recent CFL+ change since we don't need it being merged, keeping only the Windows workaround. And add the stub in place of current PNLFCFL one. This might leave us buffer for related issues.