[PATCH 0/2] backlight: lm3630a: Add a per-bank full-scale current limit

[PATCH 0/2] backlight: lm3630a: Add a per-bank full-scale current limit

[Michiel van Beers via B4 Relay]

The LM3630A driver always programs the full-scale current of both
control banks to the chip maximum of 28.25 mA. This series adds the
common led-max-microamp property to the binding and makes the driver
program it, so boards whose LEDs are rated for less can set a lower
limit.

My use case is the frontlight of the Onyx Boox Leaf e-reader (SDM636),
where Onyx's Android kernel sets the full-scale current of both banks
to 12.5 mA. The board devicetree is not upstream yet.

Patch 1 documents the property, patch 2 implements it. Both are meant
to go through the backlight tree.

Testing:
- Onyx Boox Leaf, 7.2.y kernel (sdm660-mainline) with patch 2 applied:
  led-max-microamp = <12500> on both banks reads back as code 0x0a in
  both full-scale registers, and the frontlight works normally. 5000
  and 28250 give codes 0x00 and 0x1f, with bank A visibly dimmer at
  5 mA; 28500 makes probe fail with -EINVAL. The driver in 7.4-rc1
  differs from 7.2.y only by an unrelated change in lm3630a_remove().
- dt_binding_check, and dtbs_check of all in-tree boards with an
  LM3630A (rk3566-pinenote, the i.MX6 Kobo and Tolino e-readers,
  Nexus 5, OnePlus One): no warnings for this binding.
- arm64 build with W=1 and sparse: no new warnings.

AI disclosure: I prepared this series with Claude Code (Anthropic,
Claude Opus 5.5). It drafted the driver change and the commit messages
from my description of the problem and the datasheet, and proposed the
checks above; I ran the checks and the hardware test, reviewed every
line, and take responsibility for the patches.

---
Michiel van Beers (2):
      dt-bindings: backlight: lm3630a: Add led-max-microamp
      backlight: lm3630a: Allow setting the full-scale current per bank

 .../bindings/leds/backlight/lm3630a-backlight.yaml |  9 +++++
 drivers/video/backlight/lm3630a_bl.c               | 40 +++++++++++++++++++---
 include/linux/platform_data/lm3630a_bl.h           |  4 +++
 3 files changed, 49 insertions(+), 4 deletions(-)
---
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
change-id: 20261107-lm3630a-led-max-microamp-c693253a95c5

Best regards,
--  
Michiel van Beers <michielvanbeers@gmail.com>

[PATCH 1/2] dt-bindings: backlight: lm3630a: Add led-max-microamp

[Michiel van Beers via B4 Relay]

From: Michiel van Beers <michielvanbeers@gmail.com>

The LM3630A has a full-scale current setting per control bank, from
5 mA to 28.25 mA in steps of 750 uA. Boards whose LED strings are rated
for less than the chip default of 28.25 mA have no way to describe that
limit.

Add the common led-max-microamp property to the led@0 and led@1 nodes.
The property is optional, so existing devicetrees remain valid.

Signed-off-by: Michiel van Beers <michielvanbeers@gmail.com>
---
 .../devicetree/bindings/leds/backlight/lm3630a-backlight.yaml    | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
index 6393cbf3afdf..a031679d5468 100644
--- a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
+++ b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
@@ -77,6 +77,14 @@ patternProperties:
         minimum: 0
         maximum: 255
 
+      led-max-microamp:
+        description:
+          Full-scale current of the LED strings driven by this control bank.
+          The LM3630A sets it from 5 mA to 28.25 mA in steps of 750 uA.
+        minimum: 5000
+        maximum: 28250
+        default: 28250
+
       ti,linear-mapping-mode:
         description: |
           Enable linear mapping mode. If disabled, then it will use exponential
@@ -112,6 +120,7 @@ examples:
                 label = "lcd-backlight";
                 default-brightness = <200>;
                 max-brightness = <255>;
+                led-max-microamp = <20000>;
             };
         };
     };

-- 
2.43.0

[PATCH 2/2] backlight: lm3630a: Allow setting the full-scale current per bank

[Michiel van Beers via B4 Relay]

From: Michiel van Beers <michielvanbeers@gmail.com>

The driver always programs the full-scale current of both control banks
to the maximum of 28.25 mA (code 0x1F). Boards whose LED strings are
rated for less have no way to lower it.

Read the optional led-max-microamp property of each led@ node and
program the full-scale current register of that bank with the matching
code, I_FS = 5 mA + code * 0.75 mA (datasheet SNVS974B, 7.3.1.11). The
code is rounded down, so the current never exceeds the requested value.
Values outside 5000 to 28250 uA are rejected with -EINVAL.

Without the property the driver still programs 0x1F, so existing boards
are unaffected.

Signed-off-by: Michiel van Beers <michielvanbeers@gmail.com>
---
checkpatch --strict reports errors on the two new kernel-doc lines in
lm3630a_bl.h; the hunk does not include the comment delimiters. With
-U15 it is clean.
---
 drivers/video/backlight/lm3630a_bl.c     | 40 ++++++++++++++++++++++++++++----
 include/linux/platform_data/lm3630a_bl.h |  4 ++++
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 8ef8163c7fef..1189011bb89d 100644
--- a/drivers/video/backlight/lm3630a_bl.c
+++ b/drivers/video/backlight/lm3630a_bl.c
@@ -80,6 +80,25 @@ static int lm3630a_update(struct lm3630a_chip *pchip,
 	return regmap_update_bits(pchip->regmap, reg, mask, data);
 }
 
+/*
+ * Full-scale current register code: I = 5 mA + code * 0.75 mA, code 0..31
+ * (datasheet SNVS974B, 7.3.1.11). Rounds down, so the result never exceeds
+ * the requested current. 0 means "not set" and keeps the chip default 0x1F.
+ */
+#define LM3630A_FS_CURRENT_MIN_UA	5000
+#define LM3630A_FS_CURRENT_STEP_UA	750
+#define LM3630A_FS_CURRENT_MAX_UA	28250
+#define LM3630A_FS_CURRENT_MAX_CODE	0x1F
+
+static unsigned int lm3630a_fs_current_code(unsigned int microamp)
+{
+	if (!microamp)
+		return LM3630A_FS_CURRENT_MAX_CODE;
+
+	return (microamp - LM3630A_FS_CURRENT_MIN_UA) /
+	       LM3630A_FS_CURRENT_STEP_UA;
+}
+
 /* initialize chip */
 static int lm3630a_chip_init(struct lm3630a_chip *pchip)
 {
@@ -93,10 +112,12 @@ static int lm3630a_chip_init(struct lm3630a_chip *pchip)
 	rval |= lm3630a_update(pchip, REG_CONFIG, 0x07, pdata->pwm_ctrl);
 	/* set boost control */
 	rval |= lm3630a_write(pchip, REG_BOOST, 0x38);
-	/* set current A */
-	rval |= lm3630a_update(pchip, REG_I_A, 0x1F, 0x1F);
-	/* set current B */
-	rval |= lm3630a_write(pchip, REG_I_B, 0x1F);
+	/* set full-scale current A */
+	rval |= lm3630a_update(pchip, REG_I_A, 0x1F,
+			lm3630a_fs_current_code(pdata->leda_max_microamp));
+	/* set full-scale current B */
+	rval |= lm3630a_write(pchip, REG_I_B,
+			lm3630a_fs_current_code(pdata->ledb_max_microamp));
 	/* set control */
 	rval |= lm3630a_update(pchip, REG_CTRL, 0x14, pdata->leda_ctrl);
 	rval |= lm3630a_update(pchip, REG_CTRL, 0x0B, pdata->ledb_ctrl);
@@ -472,6 +493,17 @@ static int lm3630a_parse_bank(struct lm3630a_platform_data *pdata,
 			pdata->leda_max_brt = val;
 	}
 
+	ret = fwnode_property_read_u32(node, "led-max-microamp", &val);
+	if (!ret) {
+		if (val < LM3630A_FS_CURRENT_MIN_UA ||
+		    val > LM3630A_FS_CURRENT_MAX_UA)
+			return -EINVAL;
+		if (bank)
+			pdata->ledb_max_microamp = val;
+		else
+			pdata->leda_max_microamp = val;
+	}
+
 	return 0;
 }
 
diff --git a/include/linux/platform_data/lm3630a_bl.h b/include/linux/platform_data/lm3630a_bl.h
index 530be9318711..43383c476c09 100644
--- a/include/linux/platform_data/lm3630a_bl.h
+++ b/include/linux/platform_data/lm3630a_bl.h
@@ -37,10 +37,12 @@ enum lm3630a_ledb_ctrl {
  *@leda_label    : optional led a label.
  *@leda_init_brt : led a init brightness. 4~255
  *@leda_max_brt  : led a max brightness.  4~255
+ *@leda_max_microamp : led a full-scale current, 5000~28250 uA (0: default)
  *@leda_ctrl     : led a disable, enable linear, enable exponential
  *@ledb_label    : optional led b label.
  *@ledb_init_brt : led b init brightness. 4~255
  *@ledb_max_brt  : led b max brightness.  4~255
+ *@ledb_max_microamp : led b full-scale current, 5000~28250 uA (0: default)
  *@ledb_ctrl     : led b disable, enable linear, enable exponential
  *@pwm_period    : pwm period
  *@pwm_ctrl      : pwm disable, bank a or b, active high or low
@@ -51,11 +53,13 @@ struct lm3630a_platform_data {
 	const char *leda_label;
 	int leda_init_brt;
 	int leda_max_brt;
+	unsigned int leda_max_microamp;
 	enum lm3630a_leda_ctrl leda_ctrl;
 	/* led b config. */
 	const char *ledb_label;
 	int ledb_init_brt;
 	int ledb_max_brt;
+	unsigned int ledb_max_microamp;
 	enum lm3630a_ledb_ctrl ledb_ctrl;
 	/* pwm config. */
 	unsigned int pwm_period;

-- 
2.43.0