Re: samsung-galaxybook writes to a int via a u8*

[Armin Wolf <W_Armin@gmx.de>]

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Am 28.12.25 um 12:55 schrieb Gianni Ceccarelli:

> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/platform/x86/samsung-galaxybook.c#n450
>
> `val->intval` is an int (see
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/power_supply.h#n228
> ), so writing to it via a `u8*` produces weird results, for example:
>
>      $ cat /sys/class/power_supply/BAT1/charge_control_end_threshold
>      78497792
>      $ grep END_THRESHOLD /sys/class/power_supply/BAT1/uevent
>      POWER_SUPPLY_CHARGE_CONTROL_END_THRESHOLD=-962691840
>
> The least-significant byte of numbers values contains the expected
> value:
>
>      $ perl -E 'say 78497792 & 0xFF'
>      0
>      $ perl -E 'say -962691840 & 0xFF'
>      0
>
> even after changing the threshold:
>      
>      # echo 90 >
> /sys/class/power_supply/BAT1/charge_control_end_threshold $ cat
> /sys/class/power_supply/BAT1/charge_control_end_threshold 78497882
>      $ grep END_THRESHOLD /sys/class/power_supply/BAT1/uevent
>      POWER_SUPPLY_CHARGE_CONTROL_END_THRESHOLD=-966918822
>      $ perl -E 'say 78497882 & 0xFF'
>      90
>      $ perl -E 'say -966918822 & 0xFF'
>      90
>
> I guess the code could be changed to:
>
>      u8 byteval;
>      err = charge_control_end_threshold_acpi_get(galaxybook, &byteval);
>      if (err)
>         return err;
>      val->intval = byteval;
>
> Hope this helps.
>
Thanks for your report, this pointer cast indeed seems to be the root cause of the strange values
returned by charge_control_end_threshold. I attached a patch for you to test that implements you suggestion.

Thanks,
Armin Wolf

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From cf438f40c8e954afadd7cb4a6c808bf55072561b Mon Sep 17 00:00:00 2001
From: Armin Wolf <W_Armin@gmx.de>
Date: Sun, 28 Dec 2025 21:02:18 +0100
Subject: [PATCH] platform/x86: samsung-galaxybook: Fix problematic pointer
 cast

A user reported that reading the charge threshold on his device
results in very strange values (like 78497792) being returned.
The reason for this seems to be the fact that the driver casts
the int pointer to an u8 pointer, leaving the last 3 bytes of
the destination uninitialized. Fix this by using a temporary
variable instead.

Fixes: 56f529ce4370 ("platform/x86: samsung-galaxybook: Add samsung-galaxybook driver")
Reported-by: Gianni Ceccarelli <dakkar@thenautilus.net>
Closes: https://lore.kernel.org/platform-driver-x86/20251228115556.14362d66@thenautilus.net/
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/platform/x86/samsung-galaxybook.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/samsung-galaxybook.c b/drivers/platform/x86/samsung-galaxybook.c
index 3c13e13d4885..755cb82bdb60 100644
--- a/drivers/platform/x86/samsung-galaxybook.c
+++ b/drivers/platform/x86/samsung-galaxybook.c
@@ -442,12 +442,13 @@ static int galaxybook_battery_ext_property_get(struct power_supply *psy,
 					       union power_supply_propval *val)
 {
 	struct samsung_galaxybook *galaxybook = ext_data;
+	u8 value;
 	int err;
 
 	if (psp != POWER_SUPPLY_PROP_CHARGE_CONTROL_END_THRESHOLD)
 		return -EINVAL;
 
-	err = charge_control_end_threshold_acpi_get(galaxybook, (u8 *)&val->intval);
+	err = charge_control_end_threshold_acpi_get(galaxybook, &value);
 	if (err)
 		return err;
 
@@ -455,8 +456,10 @@ static int galaxybook_battery_ext_property_get(struct power_supply *psy,
 	 * device stores "no end threshold" as 0 instead of 100;
 	 * if device has 0, report 100
 	 */
-	if (val->intval == 0)
-		val->intval = 100;
+	if (value == 0)
+		value = 100;
+
+	val->intval = value;
 
 	return 0;
 }
-- 
2.52.0