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

[David Heidelberg <david@ixit.cz>]

On 21/09/2026 13:08, Konrad Dybcio wrote:
> On 9/21/26 12:46 PM, 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>
>> ---
>>   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))
> 
> Ideally n would be wrapped in its own parentheses (doesn't
> checkpatch warn against that?)

Yeah it does, thou not sure it make sense here.
If needed, I'll send another version with it... :)

Thanks
David

> 
> Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> 
> Konrad