Re: [PATCH v2 4/5] apple-gmux: support MMIO gmux on T2 Macs

[Hans de Goede]

Hi,

On 2/18/23 13:52, Orlando Chamberlain wrote:
> On Sat, 18 Feb 2023 11:49:52 +0100
> Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> 
>> Hi,
>>
>> On 2/17/23 13:02, Orlando Chamberlain wrote:
>>> On Fri, 17 Feb 2023 11:05:31 +1100
>>> Orlando Chamberlain <orlandoch.dev@xxxxxxxxx> wrote:  
>>>>>
>>>>> Question are we not worried about MacBooks with an "APP000B"
>>>>> ACPI device (with a value IORSOURCE_MEM entry) but which do not
>>>>> actually have a gmux, because they are iGPU only ?    
>>>>
>>>> It looks like iMac20,1, iMac20,2, and iMacPro1,1 have APP000B:
>>>>
>>>> apple_gmux: Failed to find gmux I/O resource
>>>>
>>>> iMac20,2: https://linux-hardware.org/?probe=ec2af584b3&log=dmesg
>>>> iMac20,1: https://linux-hardware.org/?probe=fee7644b9c&log=dmesg
>>>> iMacPro1,1: https://linux-hardware.org/?probe=6c26c9ff8c&log=dmesg
>>>>
>>>> But I'm not sure if they actually have it or not. I'll see if I can
>>>> get people with those models to test if it's a real gmux. There
>>>> does seem to be a pattern in that those three all have AMD GPU's.  
>>>
>>> Kerem Karabay managed to find the acpi tables and macOS's ioreg
>>> from and iMacPro1,1:
>>>
>>> https://github.com/khronokernel/DarwinDumped/blob/master/iMacPro/iMacPro1%2C1/Darwin%20Dumper/DarwinDumper_3.0.4_30.12_15.30.40_iMacPro1%2C1_Apple_X64_High%20Sierra_17C2120_apple/ACPI%20Tables/DSL/DSDT.dsl#L10423
>>> https://github.com/khronokernel/DarwinDumped/blob/master/iMacPro/iMacPro1%2C1/Darwin%20Dumper/DarwinDumper_3.0.4_30.12_15.30.40_iMacPro1%2C1_Apple_X64_High%20Sierra_17C2120_apple/IORegistry/IOReg.txt#L5096
>>>
>>> The DSDT table has the same APP000B device as MacBooks with actual
>>> gmux, while the ioreg has no mention of Apple's driver
>>> AppleMuxControl2 being used for that device.
>>>
>>> I think that confirms Apple has not fixed the issue of putting
>>> APP000B's where they don't need to.
>>>
>>> Solutions to this I can think of are:
>>>
>>> - Use DMI matching to ignore product_names "iMacPro1,1" "iMac20,1",
>>>   "iMac20,2"
>>> - Maybe check if the MMIO region for gmux is filled with 0xff*
>>>
>>> *I don't know if this would work or not as I don't have a machine to
>>> check with. On my machine everything surrounding the 16 bytes used
>>> for gmux is 0xff:
>>>
>>> # hexdump -n48 -C -s 0xfe0b01f0 /dev/mem
>>> fe0b01f0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff
>>> |................| fe0b0200  00 00 3e 4f 00 00 00 00  00 00 00 00
>>> 00 00 14 00  |..>O............| fe0b0210  ff ff ff ff ff ff ff ff
>>> ff ff ff ff ff ff ff ff  |................|
>>>
>>> so maybe on the iMacPro and iMac's, this would all be 0xff.  
>>
>> Yes checking for a regular ioread32 returning 0xffffffff sounds
>> like it should work. Can you add a check for that in the next version
>> please ?  Note this means we still need to do an iomap + unmap as
>> you pointed out in another email, but I see no way around that.
> 
> I'll check that GMUX_MMIO_COMMAND_SEND (16th byte) is not 0xff, as if
> the gmux is present it will reset that to 0x00, unless a command isn't
> finished yet, in which case it will be one of 0x1, 0x4, 0x41, or 0x44.

Ok, this sounds good to me, thanks.

Regards,

Hans



>>>> I've looked at dmesg or at least lsmod on all the models with the
>>>> T2 chip and there wasn't evidence of any other models having that
>>>> error or having apple-gmux loaded on any models that shouldn't
>>>> have a gmux, other than the three mentioned above. Of course I
>>>> don't know if its possible for there to be firmware versions where
>>>> this isn't the case. 
>>>>>
>>>>> I have learned the hard way (through backlight control regressions
>>>>> in 6.1) that at least some older model MacBooks with an IO
>>>>> resource have an APP000B ACPI device without them actually having
>>>>> a gmux, these get caught by the version check and then do not
>>>>> pass the indexed check so that apple_gmux_detect() properly
>>>>> returns false.
>>>>>
>>>>> Maybe make gmux_mmio_read32() a static inline inside
>>>>> include/linux/apple-gmux.h and try to read the version here ?    
>>>>
>>>> For that would we need to ioremap() and iounmap()?  
>>>>>
>>>>> Has this been tested on iGPU only T2 Macs?    
>>>>
>>>> I don't think so. 
>>>>  
>>>>>
>>>>> Regards,
>>>>>
>>>>> Hans
>>>>>
>>>>>     
>>>>  
>>>   
>>
>