Re: [PATCH v3 5/5] platform/chrome: cros_kbd_led_backlight: support EC PWM backend

Tzung-Bi Shih
2022-05-20T04:53:34Z

On Thu, May 19, 2022 at 03:40:21PM -0700, Matthias Kaehlcke wrote:
> On Mon, Mar 21, 2022 at 04:55:47PM +0800, Tzung-Bi Shih wrote:
> > +struct keyboard_led_private {
>
> Why 'private', isn't this more a 'cros_ec_kdb_bl' or similar?

It is just drvdata. I would prefer to keep the original prefix
"keyboard_led_" if you wouldn't have strong opinion.

> > +static int
> > +keyboard_led_set_brightness_blocking_ec_pwm(struct led_classdev *cdev,
> > + enum led_brightness brightness)
>
> nit: since there is only a blocking version of .set_brightness you could omit
> 'blocking' in the function name.

Ack, will fix it in next version.

> > + struct {
> > + struct cros_ec_command msg;
> > + struct ec_params_pwm_set_keyboard_backlight params;
> > + } __packed buf;
> > + struct ec_params_pwm_set_keyboard_backlight *params = &buf.params;
> > + struct cros_ec_command *msg = &buf.msg;
> > + struct keyboard_led_private *private =
> > + container_of(cdev, struct keyboard_led_private, cdev);
> > +
> > + memset(&buf, 0, sizeof(buf));
> > +
> > + msg->version = 0;
>
> not strictly needed since you do the memset above, I guess it's
> fine to keep the assignment if you want to be explicit about the
> version.

Ack, let's remove them in next version.

> > +static int keyboard_led_init_ec_pwm(struct platform_device *pdev)
> > +{
> > + struct keyboard_led_private *private = platform_get_drvdata(pdev);
> > +
> > + private->ec = dev_get_drvdata(pdev->dev.parent);
> > + if (!private->ec) {
> > + dev_err(&pdev->dev, "no parent EC device\n");
> > + return -EINVAL;
> > + }
>
> The only thing this 'init' function does is assigning private->ec. Wouldn't
> it be clearer to do this directly in probe() from where callback is called?
> It could be with the condition that the device as a DT node.

No. The probe() isn't aware of the device is from ACPI or OF.

> Is it actually possible that the keyboard backlight device gets instantiated
> if there is no EC parent?

It shouldn't be but just in case.

> > +static const struct keyboard_led_drvdata keyboard_led_drvdata_ec_pwm = {
> > + .init = keyboard_led_init_ec_pwm_null,
>
> Is this really needed?
>
> keyboard_led_probe() checks if .init is assigned before invoking the callback:
>
> if (drvdata->init) {
> error = drvdata->init(pdev);
>
> The whole 'else' branch could be eliminated if .of_match_table of the driver
> only is assigned when CONFIG_CROS_KBD_LED_BACKLIGHT_EC_PWM is set. IMO that
> would preferable over creating 'stubs'.

CONFIG_CROS_KBD_LED_BACKLIGHT_EC_PWM and CONFIG_OF are independent. The stubs
were created to avoid compile errors if CONFIG_OF=y but
CONFIG_CROS_KBD_LED_BACKLIGHT_EC_PWM=n.

However, I just realized it could also have compile errors if CONFIG_OF=n and
CONFIG_CROS_KBD_LED_BACKLIGHT_EC_PWM=y. The `keyboard_led_drvdata_ec_pwm` is
unused.

In any case, I agree with you. Let's remove the stubs in next version. I
would use __maybe_unused for some of them.