linux-kernel - [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct multi

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Message-ID: <20250506-led-fix-v1-1-56a39b55a7fc@axis.com>
Date: Tue, 6 May 2025 12:39:32 +0200
From: Johan Adolfsson <johan.adolfsson@...s.com>
To: Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>
CC: <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Johan
 Adolfsson" <johan.adolfsson@...s.com>, <kernel@...s.com>
Subject: [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct
 multi_index

mc_subled used for multi_index needs well defined array indexes,
to guarantee the desired result, optionally 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, the previous behavior is kept, index will be in
the order nodes are processed.

Signed-off-by: Johan Adolfsson <johan.adolfsson@...s.com>
---
Since devicetree nodes are (sometimes?) processed in reverse order,
support reg as the actual multi_index index so yo get well defined
color order presented in the multi_index file.
Not sure if reusing reg for this is the correct way or if another
property such as "multi_index" or similar should be used instead.
Looks like reg is used for similar things at least.
Or should the whole "reverse the devicetree" problem be fixed instead?
---
 drivers/leds/leds-lp50xx.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/leds/leds-lp50xx.c b/drivers/leds/leds-lp50xx.c
index 02cb1565a9fb..48db024081f5 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;
 			ret = fwnode_property_read_u32(led_node, "color",
 						       &color_id);
 			if (ret) {
@@ -483,8 +484,15 @@ 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) {
+				multi_index = num_colors;
+			} else if (multi_index >= LP50XX_LEDS_PER_MODULE) {
+				dev_warn(priv->dev, "reg %i out of range\n", multi_index);
+				multi_index = num_colors;
+			}
 
-			mc_led_info[num_colors].color_index = color_id;
+			mc_led_info[multi_index].color_index = color_id;
 			num_colors++;
 		}
 

---
base-commit: 38fec10eb60d687e30c8c6b5420d86e8149f7557
change-id: 20250225-led-fix-444fb544584a

Best regards,
-- 
Johan Adolfsson <johan.adolfsson@...s.com>