linux-kernel - Re: [PATCH v4] platform: x86: Add ACPI driver for ChromeOS

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Date:   Fri, 05 Jun 2020 13:03:51 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Len Brown <lenb@...nel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        groeck@...omium.org, bleung@...omium.org, dtor@...omium.org,
        gwendal@...omium.org, vbendeb@...omium.org, andy@...radead.org,
        Ayman Bagabas <ayman.bagabas@...il.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Blaž Hrastnik <blaz@...n.io>,
        Darren Hart <dvhart@...radead.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Jeremy Soller <jeremy@...tem76.com>,
        Mattias Jacobsson <2pi@....nu>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Rajat Jain <rajatja@...gle.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v4] platform: x86: Add ACPI driver for ChromeOS

On Monday, April 13, 2020 4:12:59 PM CEST Greg Kroah-Hartman wrote:
> Meta-comment to the ACPI developers, shouldn't all of this happen
> "automatically" with the existing ACPI entries in sysfs?

I'm not quite sure what you mean by "all of this" here.

Can you please explain?

> If not, is this driver the proper way to do this?
> 
> Minor review comments below:
> 
> 
> On Mon, Apr 13, 2020 at 03:46:11PM +0200, Enric Balletbo i Serra wrote:
> > +What:		/sys/bus/acpi/devices/GGL0001:00/BINF.{0,1,4}
> > +Date:		April 2020
> > +KernelVersion:	5.8
> > +Description:
> > +		This file is reserved and doesn't shows useful information
> > +		for now.
> 
> Then do not even have it present.  sysfs should never export files that
> nothing can be done with them, userspace "knows" that if a file is not
> present, it can not use it.  Bring it back when it is useful.
> 
> > +What:		/sys/bus/acpi/devices/GGL0001:00/MECK
> > +Date:		April 2020
> > +KernelVersion:	5.8
> > +Description:
> > +		This binary file returns the SHA-1 or SHA-256 hash that is
> > +		read out of the Management Engine extend registers during
> > +		boot. The hash is exported vi ACPI so the OS can verify that
> > +		the Management Engine firmware has not changed. If Management
> > +		Engine is not present, or if the firmware was unable to read the
> > +		extend registers, this buffer can be zero.
> 
> The size is zero, or the contents are 0?
> 
> > +static char *chromeos_acpi_alloc_name(char *name, int count, int index)
> > +{
> > +	char *str;
> > +
> > +	if (count == 1)
> > +		str = kstrdup(name, GFP_KERNEL);
> > +	else
> > +		str = kasprintf(GFP_KERNEL, "%s.%d", name, index);
> 
> That's crazy, make this more obvious that "count" affects the name so
> much.  As it is, no one would know this unless they read the function
> code, and not just the name.
> 
> 
> > +/**
> > + * chromeos_acpi_add_group() - Create a sysfs group including attributes
> > + *			       representing a nested ACPI package.
> > + *
> > + * @adev: ACPI device.
> > + * @obj: Package contents as returned by ACPI.
> > + * @name: Name of the group.
> > + * @num_attrs: Number of attributes of this package.
> > + * @index: Index number of this particular group.
> > + *
> > + * The created group is called @name in case there is a single instance, or
> > + * @name.@...ex otherwise.
> > + *
> > + * All group and attribute storage allocations are included in the lists for
> > + * tracking of allocated memory.
> > + *
> > + * Return: 0 on success, negative errno on failure.
> > + */
> 
> Meta-comment, no need for kerneldoc on static functions.  It's nice to
> see, but nothing is going to notice them...
> 
> > +static int chromeos_acpi_add_method(struct acpi_device *adev, char *name)
> > +{
> > +	struct device *dev = &adev->dev;
> > +	struct acpi_buffer output;
> > +	union acpi_object *obj;
> > +	acpi_status status;
> > +	int ret = 0;
> > +
> > +	output.length = ACPI_ALLOCATE_BUFFER;
> > +
> > +	status = acpi_evaluate_object(adev->handle, name, NULL, &output);
> > +	if (ACPI_FAILURE(status)) {
> > +		dev_err(dev, "failed to retrieve %s (%d)\n", name, status);
> > +		return status;
> > +	}
> > +
> > +	obj = output.pointer;
> > +	if (obj->type == ACPI_TYPE_PACKAGE)
> > +		ret = chromeos_acpi_handle_package(adev, obj, name);
> > +
> > +	kfree(output.pointer);
> 
> Why the need for 'obj' at all in this function?  Minor nit.
> 
> > +
> > +	return ret;
> > +}
> > +
> > +static int chromeos_acpi_device_add(struct acpi_device *adev)
> > +{
> > +	struct chromeos_acpi_attribute_group *aag = chromeos_acpi.root;
> > +	struct device *dev = &adev->dev;
> > +	int i, ret;
> > +
> > +	aag = kzalloc(sizeof(*aag), GFP_KERNEL);
> > +	if (!aag)
> > +		return -ENOMEM;
> > +
> > +	INIT_LIST_HEAD(&aag->attribs);
> > +	INIT_LIST_HEAD(&aag->list);
> > +	INIT_LIST_HEAD(&chromeos_acpi.groups);
> > +
> > +	chromeos_acpi.root = aag;
> > +
> > +	/*
> > +	 * Attempt to add methods by querying the device's MLST method
> > +	 * for the list of methods.
> > +	 */
> > +	if (!chromeos_acpi_process_mlst(adev))
> > +		return 0;
> > +
> > +	dev_info(dev, "falling back to default list of methods\n");
> 
> Is this debugging code left over?  If not, make it an error, and what
> would a user be able to do with it?

Or use dev_dbg() to print it, possibly?

Cheers!