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

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Hi Enric,

On Wed, 2020-03-25 at 21:34 +0100, Enric Balletbo i Serra wrote:
> 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?
> 
So I guess your  mlst method gives list of methods you can call.
So here your can directly evaluate

- evaluate crhw.HWID


Thanks,
Srinivas



> 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
> > > >