linux-kernel - Re: [PATCH v6 1/2] leds: leds-lp50xx: Handle reg to get correct multi

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Message-ID: <eb8c858d-fde8-4916-b36c-f386242b10c4@gmail.com>
Date: Mon, 16 Jun 2025 23:29:52 +0200
From: Jacek Anaszewski <jacek.anaszewski@...il.com>
To: Johan Adolfsson <johan.adolfsson@...s.com>, Lee Jones <lee@...nel.org>,
 Pavel Machek <pavel@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Andrew Davis <afd@...com>
Cc: linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, kernel@...s.com
Subject: Re: [PATCH v6 1/2] leds: leds-lp50xx: Handle reg to get correct
 multi_index

Hi Johan,

On 6/16/25 13:25, Johan Adolfsson wrote:
> mc_subled used for multi_index needs well defined array indexes,
> to guarantee the desired result, use reg for that.
> 
> If devicetree child nodes is processed in random or reverse order
> you may end up with multi_index "blue green red" instead of the expected
> "red green blue".
> If user space apps uses multi_index to deduce how to control the leds
> they would most likely be broken without this patch if devicetree
> processing is reversed (which it appears to be).
> 
> arch/arm/boot/dts/aspeed/aspeed-bmc-facebook-fuji.dts has reg set
> but I don't see how it can have worked without this change.
> 
> If reg is not set, an error is returned,
> If reg is out of range, an error is returned.
> reg within led child nodes starts with 0, to map to the iout in each bank.
> 
> Signed-off-by: Johan Adolfsson <johan.adolfsson@...s.com>
> ---
>   drivers/leds/leds-lp50xx.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/leds/leds-lp50xx.c b/drivers/leds/leds-lp50xx.c
> index 02cb1565a9fb..344791b6c575 100644
> --- a/drivers/leds/leds-lp50xx.c
> +++ b/drivers/leds/leds-lp50xx.c
> @@ -476,6 +476,7 @@ static int lp50xx_probe_dt(struct lp50xx *priv)
>   			return -ENOMEM;
>   
>   		fwnode_for_each_child_node(child, led_node) {
> +			int multi_index = num_colors;

Any specific reason for initializing this to num_colors?

>   			ret = fwnode_property_read_u32(led_node, "color",
>   						       &color_id);
>   			if (ret) {
> @@ -483,8 +484,16 @@ static int lp50xx_probe_dt(struct lp50xx *priv)
>   				dev_err(priv->dev, "Cannot read color\n");
>   				return ret;
>   			}
> +			ret = fwnode_property_read_u32(led_node, "reg", &multi_index);
> +			if (ret != 0) {
> +				dev_err(priv->dev, "reg must be set\n");
> +				return -EINVAL;
> +			} else if (multi_index >= LP50XX_LEDS_PER_MODULE) {
> +				dev_err(priv->dev, "reg %i out of range\n", multi_index);
> +				return -EINVAL;
> +			}
>   
> -			mc_led_info[num_colors].color_index = color_id;
> +			mc_led_info[multi_index].color_index = color_id;
>   			num_colors++;
>   		}
>   
> 


Reviewed-by: Jacek Anaszewski <jacek.anaszewski@...il.com>

-- 
Best regards,
Jacek Anaszewski