Re: [PATCH v4 2/4] backlight: qcom-wled: Fix WLED3 brightness register stride

[Daniel Thompson <danielt@kernel.org>]

On Mon, Sep 21, 2026 at 12:46:23PM +0200, David Heidelberg via B4 Relay wrote:
> From: David Heidelberg <david@ixit.cz>
>
> WLED3 has a 16-bit brightness register pair per string, at 0x40 + 2*n,
> which is what the pm8941-wled driver wrote to:
>
> 	rc = regmap_bulk_write(wled->regmap,
> 			wled->addr + WLED3_CTRL_REG_VAL_BASE + 2 * i,
> 			v, 2);
>
> The restructuring for WLED3 turned that into WLED3_SINK_REG_BRIGHT(n),
> defined as 0x40 + n, so the two byte writes for consecutive strings
> overlap: string 1 overwrites the MSB of string 0 with its own LSB, and
> with the default three strings only string 1 ends up with the requested
> value.
>
> Use the 2 byte stride.
>
> Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: David Heidelberg <david@ixit.cz>

Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>


> ---
>  drivers/video/backlight/qcom-wled.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index 2281007bdd459..f452d328997ad 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -54,17 +54,17 @@
>  #define WLED3_SINK_REG_SYNC				0x47
>  #define  WLED3_SINK_REG_SYNC_CLEAR			0x00
>
>  #define WLED3_SINK_REG_CURR_SINK			0x4f
>  #define  WLED3_SINK_REG_CURR_SINK_MASK			GENMASK(7, 5)
>  #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 * 0x2))

I saw the comment about (n).

I'd rather see that in the marcos... but since the new code matches the
existing macros it has my R-b with or without change.


Daniel.