From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maximilian Luz <luzmaximilian@gmail.com>
Subject: Re: [PATCH v2 1/2] platform: Fix device check for surfacepro3_button
Date: Tue, 2 Jul 2019 03:33:20 +0200
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To: Yu Chen <yu.c.chen@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-input@vger.kernel.org, platform-driver-x86@vger.kernel.org, Dmitry Torokhov <dmitry.torokhov@gmail.com>, Hans de Goede <hdegoede@redhat.com>, Darren Hart <dvhart@infradead.org>, Andy Shevchenko <andy@infradead.org>, Benjamin Tissoires <benjamin.tissoires@redhat.com>
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On 7/2/19 3:25 AM, Maximilian Luz wrote:
> On 7/2/19 3:14 AM, Yu Chen wrote:
>> On Tue, Jul 02, 2019 at 02:37:39AM +0200, Maximilian Luz wrote:
>>> +/*
>>> + * Surface Pro 4 and Surface Book 2 / Surface Pro 2017 use the same device
>>> + * ID (MSHW0040) for the power/volume buttons. Make sure this is the right
>>> + * device by checking for the _DSM method and OEM Platform Revision.
>>> + */
>>> +static int surface_button_check_MSHW0040(struct acpi_device *dev)
>>> +{
>>> +    acpi_handle handle = dev->handle;
>>> +    union acpi_object *result;
>>> +    u64 oem_platform_rev = 0;
>>> +
>>> +    // get OEM platform revision
>>> +    result = acpi_evaluate_dsm_typed(handle, &MSHW0040_DSM_UUID,
>>> +                     MSHW0040_DSM_REVISION,
>>> +                     MSHW0040_DSM_GET_OMPR,
>>> +                     NULL, ACPI_TYPE_INTEGER);
>>> +
>> Does it mean, only 5th, 6th and newer platforms have OEM platform revision?
>> 3rd/4th will get NULL result? Or the opposite?
> 
> Correct, from my testing (with limited sample size) and AML code: 5th
> and 6th generation devices have a non-zero OEM platform revision,
> whereas 3rd and 4th gen. devices do not have any (i.e. result will be
> NULL).
> 
>>> +    if (result) {
>>> +        oem_platform_rev = result->integer.value;
>>> +        ACPI_FREE(result);
>>> +    }
>>> +
>>> +    dev_dbg(&dev->dev, "OEM Platform Revision %llu\n", oem_platform_rev);
>>> +
>>> +    return oem_platform_rev == 0 ? 0 : -ENODEV;
>> if 3rd/4th do not have this oem rev information while 5th/newer have,
>> why the latter returns NODEV(it actually has this info)?
> 
> Since we always expect a non-zero platform revision (for 5th/6th gen.),
> we can initialize it to zero and use that as "unknown"/"not available".
> So if it can not be determined, we return NODEV.

Sorry, small mistake here: If it can be determined (i.e. is 5th or 6th
gen.) then we return NODEV. Not the other way around.

Also to clarify on your last question:

On 7/2/19 3:14 AM, Yu Chen wrote:
>>   static int surface_button_add(struct acpi_device *device)
>>   {
>>   	struct surface_button *button;
>> @@ -154,6 +188,10 @@ static int surface_button_add(struct acpi_device *device)
>>   	    strlen(SURFACE_BUTTON_OBJ_NAME)))
>>   		return -ENODEV;
>>   
>> +	error = surface_button_check_MSHW0040(device);
>> +	if (error)
>> +		return error;
>> +
> ditto, 3rd/4th get error=0?

You are correct.

Maximilian