Re: [PATCH v3] platform/x86: Add driver for ACPI WMAA EC-based backlight control

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Wed, Aug 25, 2021 at 1:09 AM Daniel Dadap <ddadap@nvidia.com> wrote:
>
> A number of upcoming notebook computer designs drive the internal
> display panel's backlight PWM through the Embedded Controller (EC).
> This EC-based backlight control can be plumbed through to an ACPI
> "WMAA" method interface, which in turn can be wrapped by WMI with
> the GUID handle 603E9613-EF25-4338-A3D0-C46177516DB7.
>
> Add a new driver, aliased to the WMAA WMI GUID, to expose a sysfs
> backlight class driver to control backlight levels on systems with
> EC-driven backlights.

I tried to avoid repetition of the comments given by others.

So, mine below.

...

> +config WMAA_BACKLIGHT_WMI
> +       tristate "ACPI WMAA Backlight Driver"
> +       depends on ACPI_WMI
> +       depends on BACKLIGHT_CLASS_DEVICE
> +       help
> +         This driver provides a sysfs backlight interface for notebook
> +         systems which expose the WMAA ACPI method and an associated WMI
> +         wrapper to drive LCD backlight levels through the system's
> +         Embedded Controller.

Please, add a sentence to tell how the module will be called. There
are plenty of examples in the kernel.

...

> +struct wmaa_args {
> +       u32 set;
> +       u32 val;
> +       u32 ret;
> +       u32 ignored[3];
> +};

I guess this structure deserves a kernel doc.

...

> +static const struct wmi_device_id wmaa_backlight_wmi_id_table[] = {
> +       { .guid_string = WMAA_WMI_GUID },

> +       { },

No comma for termination.

> +};

...

> +static int wmaa_backlight_get_brightness(struct backlight_device *bd)
> +{
> +       u32 level;
> +       int ret;
> +
> +       ret = wmaa_get_brightness(&level);

> +       WARN_ON(ret != 0);

Why?

> +       return ret == 0 ? level : 0;
> +}

...

> +static int wmaa_backlight_wmi_probe(struct wmi_device *w, const void *ctx)
> +{
> +       struct backlight_properties props = {0};

{} is slightly better.

> +       struct wmi_wmaa_priv *priv;
> +       u32 source;
> +       int ret;
> +
> +       priv = devm_kmalloc(&w->dev, sizeof(*priv), GFP_KERNEL);
> +       if(!priv)
> +               return -ENOMEM;

> +       wdev = w;

I'm wondering if it's possible to avoid having a global variable.

> +       ret = wmaa_get_brightness_source(&source);
> +       if (ret)
> +               goto done;
> +
> +       if (source != WMAA_SOURCE_EC) {
> +               ret = -ENODEV;
> +               goto done;
> +       }
> +
> +       // Register a backlight handler
> +       props.type = BACKLIGHT_PLATFORM;
> +       ret = wmaa_get_max_brightness(&props.max_brightness);
> +       if (ret)
> +               goto done;
> +
> +       ret = wmaa_get_brightness(&props.brightness);
> +       if (ret)
> +               goto done;
> +
> +       priv->backlight = backlight_device_register("wmaa_backlight",
> +               NULL, NULL, &wmaa_backlight_ops, &props);
> +       if (IS_ERR(priv->backlight))
> +               return PTR_ERR(priv->backlight);
> +
> +       dev_set_drvdata(&w->dev, priv);

> +done:

Useless. Return directly.

> +       return ret;
> +}

...

> +static struct wmi_driver wmaa_backlight_wmi_driver = {
> +       .driver = {
> +               .name = "wmaa-backlight",
> +       },
> +       .probe = wmaa_backlight_wmi_probe,
> +       .remove = wmaa_backlight_wmi_remove,
> +       .id_table = wmaa_backlight_wmi_id_table,
> +};

> +

Redundant blank line.

> +module_wmi_driver(wmaa_backlight_wmi_driver);

...

> +
> +MODULE_ALIAS("wmi:"WMAA_WMI_GUID);

Can you move this closer to GUID? But I'm not sure what is the
preferred style. Hans?

-- 
With Best Regards,
Andy Shevchenko