Re: [PATCH v10] platform/chrome: Add ChromeOS ACPI device driver

From: Greg Kroah-Hartman
Date: Mon May 09 2022 - 08:46:48 EST

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In reply to: Muhammad Usama Anjum: "[PATCH v10] platform/chrome: Add ChromeOS ACPI device driver"
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On Mon, May 09, 2022 at 04:35:48PM +0500, Muhammad Usama Anjum wrote:
> From: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
>
> The x86 Chromebooks have the ChromeOS ACPI device. This driver attaches
> to the ChromeOS ACPI device and exports the values reported by ACPI in a
> sysfs directory. This data isn't present in ACPI tables when read
> through ACPI tools, hence a driver is needed to do it. The driver gets
> data from firmware using the ACPI component of the kernel. The ACPI values
> are presented in string form (numbers as decimal values) or binary
> blobs, and can be accessed as the contents of the appropriate read only
> files in the standard ACPI device's sysfs directory tree. This data is
> consumed by the ChromeOS user space.
>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> Co-developed-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> ---
> The driver's implementation has been changed completely after Greg's
> comment. I've updated the authorship of the module to myself. Enric,
> Please let me know if yuo are comfortable with this.
>
> Changes in v10:
> - Remove COMPILE_TEST as driver depends on ACPI component which isn't
> enabled by COMPILE_TEST itself.
> - Fix build warnings
>
> Changes in v9:
> - Changed the implementation completely
> - Move the driver to drivers/platform/chrome
> - Remove Acked-by Rafael as driver has changed
> - Corrected some typos
> - Changed the author of the module
>
> Changes in v8:
> - Change struct platform_driver name from chromeos_acpi_driver to
> chromeos_acpi_device_driver
>
> Changes in v7:
> - Rename acpi_chromeos Kconfig option to chromeos_acpi
> - Change this acpi driver to platform driver
> - Minor cosmetic changes
>
> There were the following concerns on v4 which have been delt with in
> v5/v6:
> - Remove BINF.{0,1,4} from sysfs as they are reserved and not used
> anymore
> - Reword the description of MECK
> - Change function name from chromeos_acpi_alloc_name() to
> chromeos_acpi_gen_file_name()
> - Remove local variable obj in chromeos_acpi_add_method()
> - Replace usage of dev_info() to dev_dbg()
> - Improve the description of the patch
> - Add the firmware interface document which serves as primary
> documentation and garantees that this interface will not change
> - GGL0001 is valid PNP ID of the Google. PNP ID can be used with the
> ACPI devices. Consensus was developed on it in discussion of v4.
>
> Changes in v6:
> - Correct authorship and path email's From
> - Add changelog between v4 and v5 in detail
> - Add copywrite year 2022
> - Improve the description and add concerns from V4 which have been fixed
>
> Changes in v5:
> - Improve the description of the patch
> - Document firmware interface
> - Update sysfs interface documentation
> - Remove binf{0,1,4} as they have been deprecated
> - Update some cleanup logic in case of error
> - Remove freeing of chromeos_acpi.root explicitely in
> chromeos_acpi_device_remove() as it'll be automatically freed by
> chromeos_acpi_remove_groups()
> - If sysfs_create_groups() fails in chromeos_acpi_process_mlst(),
> cleanup all groups
> - Cosmetic changes
>
> Changes in v4:
> https://lore.kernel.org/lkml/20200413134611.478441-1-enric.balletbo@xxxxxxxxxxxxx/t/
> - Add COMPILE_TEST to increase build coverage.
> - Add sysfs ABI documentation.
> - Rebased on top of 5.7-rc1 and solve conflicts.
> - Cc ACPI maintainers.
>
> Changes in v3:
> - Use attribute groups instead of adding files "by hand".
> - Do not use "raw" kobject to create directories.
> - Do not abuse of the platform_device interface. Remove it.
>
> Changes in v2:
> - Note that this version is a total rework, with those major changes:
> - Use lists to track dinamically allocated attributes and groups.
> - Use sysfs binary attributes to store the ACPI contents.
> - Remove all the functionalities except the one that creates the sysfs files.
> ---
> .../ABI/testing/sysfs-driver-chromeos-acpi | 126 ++++++
> .../acpi/chromeos-acpi-device.rst | 363 ++++++++++++++++++
> Documentation/firmware-guide/acpi/index.rst | 1 +
> drivers/platform/chrome/Kconfig | 11 +
> drivers/platform/chrome/Makefile | 1 +
> drivers/platform/chrome/chromeos_acpi.c | 278 ++++++++++++++
> 6 files changed, 780 insertions(+)
> create mode 100644 Documentation/ABI/testing/sysfs-driver-chromeos-acpi
> create mode 100644 Documentation/firmware-guide/acpi/chromeos-acpi-device.rst
> create mode 100644 drivers/platform/chrome/chromeos_acpi.c
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-chromeos-acpi b/Documentation/ABI/testing/sysfs-driver-chromeos-acpi
> new file mode 100644
> index 0000000000000..5b59ef9d7b371
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-driver-chromeos-acpi
> @@ -0,0 +1,126 @@
> +What: /sys/bus/platform/devices/GGL0001:*/BINF.2
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows information about the current boot of
> + the active EC firmware.
> + * 0 - Read only (recovery) firmware.
> + * 1 - Rewritable firmware.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/BINF.3
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows information about the current boot of
> + the active main firmware type.
> + * 0 - Recovery.
> + * 1 - Normal.
> + * 2 - Developer.
> + * 3 - Netboot (factory installation only).
> +
> +What: /sys/bus/platform/devices/GGL0001:*/CHSW
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the switch position for the Chrome OS specific
> + hardware switches.
> + * 0 - No changes.
> + * 2 - Recovery button was pressed when firmware booted.
> + * 4 - Recovery button was pressed when EC firmware booted.
> + * 32 - Developer switch was enabled when firmware booted.
> + * 512 - Firmware write protection was disabled when firmware
> + booted.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/FMAP
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the physical memory address of the start of
> + the main processor firmware flashmap.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/FRID
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the firmware version for the read-only portion
> + of the main processor firmware.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/FWID
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the firmware version for the rewritable portion
> + of the main processor firmware.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/GPIO.X/GPIO.0
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the type of the GPIO signal for the Chrome OS
> + specific GPIO assignments.
> + * 1 - Recovery button.
> + * 2 - Developer mode switch.
> + * 3 - Firmware write protection switch.
> + * 256 to 511 - Debug header GPIO 0 to GPIO 255.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/GPIO.X/GPIO.1
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the signal attributes of the GPIO signal.
> + * 0 - Signal is active low.
> + * 1 - Signal is active high.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/GPIO.X/GPIO.2
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the GPIO number on the specified GPIO
> + controller.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/GPIO.X/GPIO.3
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the name of the GPIO controller.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/HWID
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the hardware ID for the Chromebook.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/MECK
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This binary file returns the SHA-1 or SHA-256 hash that is
> + read out of the Management Engine extended 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
> + extended registers, this buffer size can be zero.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/VBNV.0
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the offset in CMOS bank 0 of the verified boot
> + non-volatile storage block, counting from the first writable
> + CMOS byte (that is, 'offset = 0' is the byte following the 14
> + bytes of clock data).
> +
> +What: /sys/bus/platform/devices/GGL0001:*/VBNV.1
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This file shows the size in bytes of the verified boot
> + non-volatile storage block.
> +
> +What: /sys/bus/platform/devices/GGL0001:*/VDAT
> +Date: May 2022
> +KernelVersion: 5.19
> +Description:
> + This binary file returns the verified boot data block shared
> + between the firmware verification step and the kernel
> + verification step.
> diff --git a/Documentation/firmware-guide/acpi/chromeos-acpi-device.rst b/Documentation/firmware-guide/acpi/chromeos-acpi-device.rst
> new file mode 100644
> index 0000000000000..f37fc90ce340e
> --- /dev/null
> +++ b/Documentation/firmware-guide/acpi/chromeos-acpi-device.rst
> @@ -0,0 +1,363 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================
> +Chrome OS ACPI Device
> +=====================
> +
> +Hardware functionality specific to Chrome OS is exposed through a Chrome OS ACPI device.
> +The plug and play ID of a Chrome OS ACPI device is GGL0001. GGL is a valid PNP ID of Google.
> +PNP ID can be used with the ACPI devices according to the guidelines. The following ACPI
> +objects are supported:
> +
> +.. flat-table:: Supported ACPI Objects
> + :widths: 1 2
> + :header-rows: 1
> +
> + * - Object
> + - Description
> +
> + * - CHSW
> + - Chrome OS switch positions
> +
> + * - HWID
> + - Chrome OS hardware ID
> +
> + * - FWID
> + - Chrome OS firmware version
> +
> + * - FRID
> + - Chrome OS read-only firmware version
> +
> + * - BINF
> + - Chrome OS boot information
> +
> + * - GPIO
> + - Chrome OS GPIO assignments
> +
> + * - VBNV
> + - Chrome OS NVRAM locations
> +
> + * - VDTA
> + - Chrome OS verified boot data
> +
> + * - FMAP
> + - Chrome OS flashmap base address
> +
> + * - MLST
> + - Chrome OS method list
> +
> +CHSW (Chrome OS switch positions)
> +=================================
> +This control method returns the switch positions for Chrome OS specific hardware switches.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +An integer containing the switch positions as bitfields:
> +
> +.. flat-table::
> + :widths: 1 2
> +
> + * - 0x00000002
> + - Recovery button was pressed when x86 firmware booted.
> +
> + * - 0x00000004
> + - Recovery button was pressed when EC firmware booted. (required if EC EEPROM is
> + rewritable; otherwise optional)
> +
> + * - 0x00000020
> + - Developer switch was enabled when x86 firmware booted.
> +
> + * - 0x00000200
> + - Firmware write protection was disabled when x86 firmware booted. (required if
> + firmware write protection is controlled through x86 BIOS; otherwise optional)
> +
> +All other bits are reserved and should be set to 0.
> +
> +HWID (Chrome OS hardware ID)
> +============================
> +This control method returns the hardware ID for the Chromebook.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A null-terminated ASCII string containing the hardware ID from the Model-Specific Data area of
> +EEPROM.
> +
> +Note that the hardware ID can be up to 256 characters long, including the terminating null.
> +
> +FWID (Chrome OS firmware version)
> +=================================
> +This control method returns the firmware version for the rewritable portion of the main
> +processor firmware.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A null-terminated ASCII string containing the complete firmware version for the rewritable
> +portion of the main processor firmware.
> +
> +FRID (Chrome OS read-only firmware version)
> +===========================================
> +This control method returns the firmware version for the read-only portion of the main
> +processor firmware.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A null-terminated ASCII string containing the complete firmware version for the read-only
> +(bootstrap + recovery ) portion of the main processor firmware.
> +
> +BINF (Chrome OS boot information)
> +=================================
> +This control method returns information about the current boot.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +
> +.. code-block::
> +
> + Package {
> + Reserved1
> + Reserved2
> + Active EC Firmware
> + Active Main Firmware Type
> + Reserved5
> + }
> +
> +.. flat-table::
> + :widths: 1 1 2
> + :header-rows: 1
> +
> + * - Field
> + - Format
> + - Description
> +
> + * - Reserved1
> + - DWORD
> + - Set to 256 (0x100). This indicates this field is no longer used.
> +
> + * - Reserved2
> + - DWORD
> + - Set to 256 (0x100). This indicates this field is no longer used.
> +
> + * - Active EC firmware
> + - DWORD
> + - The EC firmware which was used during boot.
> +
> + - 0 - Read-only (recovery) firmware
> + - 1 - Rewritable firmware.
> +
> + Set to 0 if EC firmware is always read-only.
> +
> + * - Active Main Firmware Type
> + - DWORD
> + - The main firmware type which was used during boot.
> +
> + - 0 - Recovery
> + - 1 - Normal
> + - 2 - Developer
> + - 3 - netboot (factory installation only)
> +
> + Other values are reserved.
> +
> + * - Reserved5
> + - DWORD
> + - Set to 256 (0x100). This indicates this field is no longer used.
> +
> +GPIO (Chrome OS GPIO assignments)
> +=================================
> +This control method returns information about Chrome OS specific GPIO assignments for
> +Chrome OS hardware, so the kernel can directly control that hardware.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +.. code-block::
> +
> + Package {
> + Package {
> + // First GPIO assignment
> + Signal Type //DWORD
> + Attributes //DWORD
> + Controller Offset //DWORD
> + Controller Name //ASCIIZ
> + },
> + ...
> + Package {
> + // Last GPIO assignment
> + Signal Type //DWORD
> + Attributes //DWORD
> + Controller Offset //DWORD
> + Controller Name //ASCIIZ
> + }
> + }
> +
> +Where ASCIIZ means a null-terminated ASCII string.
> +
> +.. flat-table::
> + :widths: 1 1 2
> + :header-rows: 1
> +
> + * - Field
> + - Format
> + - Description
> +
> + * - Signal Type
> + - DWORD
> + - Type of GPIO signal
> +
> + - 0x00000001 - Recovery button
> + - 0x00000002 - Developer mode switch
> + - 0x00000003 - Firmware write protection switch
> + - 0x00000100 - Debug header GPIO 0
> + - ...
> + - 0x000001FF - Debug header GPIO 255
> +
> + Other values are reserved.
> +
> + * - Attributes
> + - DWORD
> + - Signal attributes as bitfields:
> +
> + - 0x00000001 - Signal is active-high (for button, a GPIO value
> + of 1 means the button is pressed; for switches, a GPIO value
> + of 1 means the switch is enabled). If this bit is 0, the signal
> + is active low. Set to 0 for debug header GPIOs.
> +
> + * - Controller Offset
> + - DWORD
> + - GPIO number on the specified controller.
> +
> + * - Controller Name
> + - ASCIIZ
> + - Name of the controller for the GPIO.
> + Currently supported names:
> + "NM10" - Intel NM10 chip
> +
> +VBNV (Chrome OS NVRAM locations)
> +================================
> +This control method returns information about the NVRAM (CMOS) locations used to
> +communicate with the BIOS.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +.. code-block::
> +
> + Package {
> + NV Storage Block Offset //DWORD
> + NV Storage Block Size //DWORD
> + }
> +
> +.. flat-table::
> + :widths: 1 1 2
> + :header-rows: 1
> +
> + * - Field
> + - Format
> + - Description
> +
> + * - NV Storage Block Offset
> + - DWORD
> + - Offset in CMOS bank 0 of the verified boot non-volatile storage block, counting from
> + the first writable CMOS byte (that is, offset=0 is the byte following the 14 bytes of
> + clock data).
> +
> + * - NV Storage Block Size
> + - DWORD
> + - Size in bytes of the verified boot non-volatile storage block.
> +
> +FMAP (Chrome OS flashmap address)
> +=================================
> +This control method returns the physical memory address of the start of the main processor
> +firmware flashmap.
> +
> +Arguments:
> +----------
> +None
> +
> +NoneResult code:
> +----------------
> +A DWORD containing the physical memory address of the start of the main processor firmware
> +flashmap.
> +
> +VDTA (Chrome OS verified boot data)
> +===================================
> +This control method returns the verified boot data block shared between the firmware
> +verification step and the kernel verification step.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A buffer containing the verified boot data block.
> +
> +MECK (Management Engine Checksum)
> +=================================
> +This control method returns the SHA-1 or SHA-256 hash that is read out of the Management
> +Engine extended registers during boot. The hash is exported via ACPI so the OS can verify that
> +the ME firmware has not changed. If Management Engine is not present, or if the firmware was
> +unable to read the extended registers, this buffer can be zero.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A buffer containing the ME hash.
> +
> +MLST (Chrome OS method list)
> +============================
> +This control method returns a list of the other control methods supported by the Chrome OS
> +hardware device.
> +
> +Arguments:
> +----------
> +None
> +
> +Result code:
> +------------
> +A package containing a list of null-terminated ASCII strings, one for each control method
> +supported by the Chrome OS hardware device, not including the MLST method itself.
> +For this version of the specification, the result is:
> +
> +.. code-block::
> +
> + Package {
> + "CHSW",
> + "FWID",
> + "HWID",
> + "FRID",
> + "BINF",
> + "GPIO",
> + "VBNV",
> + "FMAP",
> + "VDTA",
> + "MECK"
> + }
> diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> index b053b0c3d6969..b6a42f4ffe032 100644
> --- a/Documentation/firmware-guide/acpi/index.rst
> +++ b/Documentation/firmware-guide/acpi/index.rst
> @@ -29,3 +29,4 @@ ACPI Support
> non-d0-probe
> extcon-intel-int3496
> intel-pmc-mux
> + chromeos-acpi-device
> diff --git a/drivers/platform/chrome/Kconfig b/drivers/platform/chrome/Kconfig
> index 75e93efd669f0..717299cbccac6 100644
> --- a/drivers/platform/chrome/Kconfig
> +++ b/drivers/platform/chrome/Kconfig
> @@ -15,6 +15,17 @@ menuconfig CHROME_PLATFORMS
>
> if CHROME_PLATFORMS
>
> +config CHROMEOS_ACPI
> + tristate "ChromeOS specific ACPI extensions"
> + depends on ACPI
> + help
> + This driver provides the firmware interface for the services
> + exported through the ChromeOS interfaces when using ChromeOS
> + ACPI firmware.
> +
> + If you have an ACPI-compatible Chromebook, say Y or M here.
> + The module will be called chromeos_acpi.
> +
> config CHROMEOS_LAPTOP
> tristate "Chrome OS Laptop"
> depends on I2C && DMI && X86
> diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
> index 6420ca129548e..52f5a2dde8b81 100644
> --- a/drivers/platform/chrome/Makefile
> +++ b/drivers/platform/chrome/Makefile
> @@ -4,6 +4,7 @@
> CFLAGS_cros_ec_trace.o:= -I$(src)
> CFLAGS_cros_ec_sensorhub_ring.o:= -I$(src)
>
> +obj-$(CONFIG_CHROMEOS_ACPI) += chromeos_acpi.o
> obj-$(CONFIG_CHROMEOS_LAPTOP) += chromeos_laptop.o
> obj-$(CONFIG_CHROMEOS_PRIVACY_SCREEN) += chromeos_privacy_screen.o
> obj-$(CONFIG_CHROMEOS_PSTORE) += chromeos_pstore.o
> diff --git a/drivers/platform/chrome/chromeos_acpi.c b/drivers/platform/chrome/chromeos_acpi.c
> new file mode 100644
> index 0000000000000..cb7b6d326803d
> --- /dev/null
> +++ b/drivers/platform/chrome/chromeos_acpi.c
> @@ -0,0 +1,278 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * ChromeOS specific ACPI extensions
> + *
> + * Copyright 2022 Google LLC
> + *
> + * This driver attaches to the ChromeOS ACPI device and then exports the
> + * values reported by the ACPI in a sysfs directory. All values are
> + * presented in the string form (numbers as decimal values) and can be
> + * accessed as the contents of the appropriate read only files in the
> + * sysfs directory tree.
> + */
> +#include <linux/acpi.h>
> +#include <linux/platform_device.h>
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +
> +#define ACPI_ATTR_NAME_LEN 4
> +
> +#define DEV_ATTR(_var, _name) \
> + static struct device_attribute dev_attr_##_var = { \
> + .attr = { .name = _name, .mode = 0444 }, \
> + .show = chromeos_first_level_attr_show \
> + };

Why do you really need to define your own macro here?

What's wrong with DEVICE_ATTR_RO()?

At the very least, use __ATTR() please, to ensure you get the
read-only mode correct, but really, just use the macros we have already
today. I see you want only one show function, so please use
__ATTR().

> +
> +#define GPIO_ATTR_GROUP(_group, _name, _num) \
> + static umode_t attr_is_visible_gpio_##_num(struct kobject *kobj, \
> + struct attribute *attr, int n) \
> + { \
> + if (_num < chromeos_acpi_gpio_groups) \
> + return attr->mode; \
> + else \
> + return 0; \
> + } \
> + static ssize_t chromeos_attr_show_gpio_##_num(struct device *dev, \
> + struct device_attribute *attr, \
> + char *buf) \
> + { \
> + char name[ACPI_ATTR_NAME_LEN + 1]; \
> + int ret, num; \
> + \
> + ret = parse_attr_name(attr->attr.name, name, &num); \
> + if (ret) \
> + return ret; \
> + ret = chromeos_acpi_evaluate_method(dev, _num, num, name, buf); \
> + if (ret < 0) \
> + ret = 0; \
> + return ret; \
> + } \
> + static struct device_attribute dev_attr_0_##_group = { \
> + .attr = { .name = "GPIO.0", .mode = 0444 }, \
> + .show = chromeos_attr_show_gpio_##_num \
> + }; \
> + static struct device_attribute dev_attr_1_##_group = { \
> + .attr = { .name = "GPIO.1", .mode = 0444 }, \
> + .show = chromeos_attr_show_gpio_##_num \
> + }; \
> + static struct device_attribute dev_attr_2_##_group = { \
> + .attr = { .name = "GPIO.2", .mode = 0444 }, \
> + .show = chromeos_attr_show_gpio_##_num \
> + }; \
> + static struct device_attribute dev_attr_3_##_group = { \
> + .attr = { .name = "GPIO.3", .mode = 0444 }, \
> + .show = chromeos_attr_show_gpio_##_num \
> + }; \

Same for the above, __ATTR() please.

> + static struct attribute *attrs_##_group[] = { \
> + &dev_attr_0_##_group.attr, \
> + &dev_attr_1_##_group.attr, \
> + &dev_attr_2_##_group.attr, \
> + &dev_attr_3_##_group.attr, \
> + NULL \
> + }; \
> + static const struct attribute_group attr_group_##_group = { \
> + .name = _name, \
> + .is_visible = attr_is_visible_gpio_##_num, \
> + .attrs = attrs_##_group \
> + };
> +
> +static unsigned int chromeos_acpi_gpio_groups;
> +
> +/* Parse the ACPI package and return the data related to that attribute */
> +static int chromeos_acpi_handle_package(struct device *dev, union acpi_object *obj,
> + int pkg_num, int sub_pkg_num, char *name, char *buf)
> +{
> + union acpi_object *element = obj->package.elements;
> + int length = -EINVAL;
> +
> + if (pkg_num >= obj->package.count)
> + return -EINVAL;
> + element += pkg_num;
> +
> + if (element->type == ACPI_TYPE_PACKAGE) {
> + if (sub_pkg_num >= element->package.count)
> + return -EINVAL;
> + // select sub element inside this package
> + element = element->package.elements;
> + element += sub_pkg_num;
> + }
> +
> + switch (element->type) {
> + case ACPI_TYPE_INTEGER:
> + length = sysfs_emit(buf, "%d", (int)element->integer.value);

Why not just:
return sysfs_emit(....)
here and below?

That allows you to drop the length variable entirely.

> + break;
> + case ACPI_TYPE_STRING:
> + length = sysfs_emit(buf, "%s", element->string.pointer);
> + break;
> + case ACPI_TYPE_BUFFER:
> + length = sysfs_emit(buf, "%s", element->buffer.pointer);
> + break;
> + default:
> + dev_err(dev, "element type %d not supported\n", element->type);
> + break;
> + }
> +
> + return length;
> +}

But that all is just minor tweaks, your call if you want to do that or
not. Otherwise looks much better than originally, nice work:

Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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