Re: [PATCH 1/2] HID: apple: preserve keyboard backlight across T2 resume

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Removing the `LED_CORE_SUSPENDRESUME` flag reverts a previous power-management fix, causing the keyboard backlight to remain powered on during system suspend.
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--- Patch [1]: [PATCH 1/2] HID: apple: preserve keyboard backlight across T2 resume ---
commit 2758811c67b214fbd3316fec3f21127f8166f490
Author: Andre Eikmeyer <dev@deq.rocks>

HID: apple: preserve keyboard backlight across T2 resume

This commit fixes an issue where the T2 virtual USB host controller
re-enumerates the internal keyboard on resume, resulting in the backlight
starting off. It caches the brightness during removal and restores it
during the subsequent probe.

Fixes: 1f95a6cd5ad7 ("HID: apple: ensure the keyboard backlight is off if suspending")
Cc: stable@vger.kernel.org

> diff --git a/drivers/hid/hid-apple.c b/drivers/hid/hid-apple.c
> --- a/drivers/hid/hid-apple.c
> +++ b/drivers/hid/hid-apple.c

[ ... ]

> @@ -860,13 +864,20 @@ static int apple_backlight_init(struct hid_device *hdev)
>  	asc->backlight->cdev.name = "apple::kbd_backlight";
>  	asc->backlight->cdev.max_brightness = rep->backlight_on_max;
>  	asc->backlight->cdev.brightness_set_blocking = apple_backlight_led_set;
> -	asc->backlight->cdev.flags = LED_CORE_SUSPENDRESUME;
> +	/* VHCI re-enumeration restores the cached brightness in the next probe. */

[Severity: High]
Does removing the LED_CORE_SUSPENDRESUME flag cause the backlight to remain
on during system suspend?

The T2 butterfly keyboard hardware does not automatically power off its
backlight when suspending. When this flag is removed, the LED subsystem
bypasses led_classdev_suspend(), leaving the hardware illuminated and
draining the battery.

The new caching mechanism in apple_remove() successfully tracks the user
brightness preference, as led_classdev_suspend() only alters the physical
hardware state without modifying the logical led_cdev->brightness.

Could the device initialization issue have been caused by the hardcoded
apple_backlight_set(hdev, 0, 0) during probe, rather than the presence of
this suspend flag?

>  
> -	ret = apple_backlight_set(hdev, 0, 0);

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Sashiko AI review · https://sashiko.dev/#/patchset/20260718121527.15924-1-dev@deq.rocks?part=1