Re: [PATCH v2 1/3] backlight: qcom-wled: Fix WLED3 brightness register stride

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The patch incorrectly implements a 16-byte stride for WLED3 brightness registers instead of the intended 2-byte stride, causing register collision and corruption.
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commit f7a2ef410d595586ca0ef2c87637e54f23dec1e2
Author: David Heidelberg <david@ixit.cz>
Subject: backlight: qcom-wled: Fix WLED3 brightness register stride

This commit aims to fix an overlapping brightness register write issue in the
WLED3 driver. It modifies the WLED3_SINK_REG_BRIGHT macro to update the
register stride for consecutive strings. The commit message states the intent
is to use a 2-byte stride.

> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index 650dd95f06ef5..22c35da72dce3 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -59,7 +59,7 @@
>  #define  WLED3_SINK_REG_CURR_SINK_SHFT			5
>  
>  /* WLED3 specific per-'string' registers below */
> -#define WLED3_SINK_REG_BRIGHT(n)			(0x40 + n)
> +#define WLED3_SINK_REG_BRIGHT(n)			(0x40 + (n * 0x10))

[Severity: High]
Does this code incorrectly implement a 16-byte stride instead of the intended
2-byte stride?

The commit message states "Use the 2 byte stride.", but the macro evaluates to
a 16-byte stride (n * 0x10) instead of a mathematically sound 2-byte stride
(n * 2).

When wled3_set_brightness() evaluates this macro and passes it to
regmap_bulk_write():

drivers/video/backlight/qcom-wled.c:wled3_set_brightness() {
    ...
		rc = regmap_bulk_write(wled->regmap, wled->ctrl_addr +
				       WLED3_SINK_REG_BRIGHT(wled->cfg.enabled_strings[i]),
				       &v, sizeof(v));
    ...
}

Writing 2 bytes to WLED3_SINK_REG_BRIGHT(2) calculates the address as
0x40 + 0x20 = 0x60. This will overwrite the adjacent control register
WLED3_SINK_REG_STR_MOD_EN(0) (which is also defined as 0x60 + 0x00), causing
hardware control register corruption.

>  
>  #define WLED3_SINK_REG_STR_MOD_EN(n)			(0x60 + (n * 0x10))
>  #define  WLED3_SINK_REG_STR_MOD_MASK			BIT(7)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260914-qcom-wled-backlight-v2-0-a908d9233e93@ixit.cz?part=1