linux-kernel - Re: [PATCH v2] platform: x86: Add ACPI driver for ChromeOS

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Message-ID: <fbd5e95a-59ab-bb51-892e-ddd220b85215@collabora.com>
Date:   Wed, 25 Mar 2020 21:34:49 +0100
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, vbendeb@...omium.org,
        groeck@...omium.org, bleung@...omium.org, dtor@...omium.org,
        gwendal@...omium.org, andy@...radead.org,
        Collabora Kernel ML <kernel@...labora.com>,
        Ayman Bagabas <ayman.bagabas@...il.com>,
        Darren Hart <dvhart@...radead.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jeremy Soller <jeremy@...tem76.com>,
        Mattias Jacobsson <2pi@....nu>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Rajat Jain <rajatja@...gle.com>,
        Yauhen Kharuzhy <jekhor@...il.com>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v2] platform: x86: Add ACPI driver for ChromeOS

Hi Srinivas,

On 24/3/20 18:20, Srinivas Pandruvada wrote:
> On Tue, 2020-03-24 at 18:08 +0100, Enric Balletbo i Serra wrote:
>> Hi Greg,
>>
>> On 24/3/20 17:49, Greg Kroah-Hartman wrote:
>>> On Tue, Mar 24, 2020 at 05:31:10PM +0100, Enric Balletbo i Serra
>>> wrote:
>>>> Hi Greg,
>>>>
>>>> Many thanks for your quick answer, some comments below.
>>>>
> [...]
> 
>>> Are you sure they aren't already there under
>>> /sys/firmware/acpi/?  I
>>> thought all tables and methods were exported there with no need to
>>> do
>>> anything special.
>>>
>>
>> That's the first I did when I started to forward port this patch from
>> chromeos
>> kernel to mainline.
>>
>> On my system I get:
>>
>> /sys/firmware/acpi/tables#
>> APIC  DSDT  FACP  FACS  HPET  MCFG  SSDT  data  dynamic
>>
>> (data and dynamic are empty directories)
>>
>> I quickly concluded (maybe wrong) that as there is no a MLST entry it
>> was not
>> exported, but maybe one of those already contains the info? Or,
>> should I expect
>> a MLST entry here?
>>
> If the data you are reading doesn't depend on any runtime variable in
> ACPI tables then you can read from firmware tables as is.
> 
> You can download acpica tools and run your method on acpi dump using
> acpiexec tool. Once you can take dump, you can run on any Linux system.
> 
> If you can get what you need from running on the dump, then you can do
> by directly reading from /sys/firmware/acpi/tables/ from user space
> without kernel change. Sometimes it is enough as lots of config data
> tend to be static.
> 

As I said I'm not an ACPI expert, so thanks in advance for your help.

I am trying to look if I can get from userspace the value of the HWID entry
exported from the driver.

$ cat /sys/devices/platform/chromeos_acpi/HWID
SAMUS E25-G7R-W35

Using acpiexec I get the element list of the MLST method, but I don't know how
to get the HWID value.

- evaluate crhw.mlst
Evaluating \CRHW.MLST
Evaluation of \CRHW.MLST returned object 0x55f17a7aed60, external buffer length 158
  [Package] Contains 10 Elements:
    [String] Length 04 = "CHSW"
    [String] Length 04 = "FWID"
    [String] Length 04 = "HWID"
    [String] Length 04 = "FRID"
    [String] Length 04 = "BINF"
    [String] Length 04 = "GPIO"
    [String] Length 04 = "VBNV"
    [String] Length 04 = "VDAT"
    [String] Length 04 = "FMAP"
    [String] Length 04 = "MECK"

Any clue?

Thanks in advance,
Enric


> Thanks,
> Srinivas
> 
> 
> 
> 
> 
> 
>>> What makes these attributes "special" from any other ACPI method?
>>>
>>
>> I can't answer this question right now. I need to investigate more I
>> guess ;-)
>>
>> Thanks again for your answer,
>> Enric
>>
>>>>>> +static int __init chromeos_acpi_init(void)
>>>>>> +{
>>>>>> +	int ret;
>>>>>> +
>>>>>> +	chromeos_acpi.pdev =
>>>>>> platform_device_register_simple("chromeos_acpi",
>>>>>> +						PLATFORM_DEVID_
>>>>>> NONE, NULL, 0);
>>>>>> +	if (IS_ERR(chromeos_acpi.pdev)) {
>>>>>> +		pr_err("unable to register chromeos_acpi
>>>>>> platform device\n");
>>>>>> +		return PTR_ERR(chromeos_acpi.pdev);
>>>>>> +	}
>>>>>
>>>>> Only use platform devices and drivers for things that are
>>>>> actually
>>>>> platform devices and drivers.  That's not what this is, it is
>>>>> an ACPI
>>>>> device and driver.  Don't abuse the platform interface please.
>>>>>
>>>>
>>>> Ok. The purpose was to not break ChromeOS userspace since is
>>>> looking for the
>>>> attributes inside /sys/devices/platform/chromeos_acpi. Not a good
>>>> reason, I
>>>> know, and I assume we will need to change userspace instead, and
>>>> convert this to
>>>> a ACPI device and driver only, right?
>>>
>>> How can any userspace be looking for anything that hasn't been
>>> submitted
>>> before?  That's nothing to worry about, we don't have to support
>>> things
>>> like that :)
>>>
>>>> I'll investigate the different places in userspace where this is
>>>> used and see
>>>> how difficult it is to do the changes.
>>>
>>> Look at /sys/firmware/acpi/ first please.
>>>
>>> thanks,
>>>
>>> greg k-h
>>>
> 
>