Re: [PATCH v2 8/9] leds: add LM3633 driver
From: Kim, Milo
Date: Mon Nov 30 2015 - 03:49:05 EST
Hi Jacek,
Thanks for your detailed feedback. Please refer to my comments below.
On 11/27/2015 8:19 PM, Jacek Anaszewski wrote:
Hi Milo,
Thanks for the update. I have few comments below.
diff --git a/drivers/leds/leds-lm3633.c b/drivers/leds/leds-lm3633.c
new file mode 100644
index 0000000..9c391ca
--- /dev/null
+++ b/drivers/leds/leds-lm3633.c
@@ -0,0 +1,840 @@
+/*
+ * TI LM3633 LED driver
+ *
+ * Copyright 2015 Texas Instruments
+ *
+ * Author: Milo Kim <milo.kim@xxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/leds.h>
+#include <linux/mfd/ti-lmu.h>
+#include <linux/mfd/ti-lmu-register.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#define LM3633_MAX_PWM 255
+#define LM3633_MIN_CURRENT 5000
+#define LM3633_MAX_CURRENT 30000
+#define LM3633_MAX_PERIOD 9700
+#define LM3633_SHORT_TIMESTEP 16
+#define LM3633_LONG_TIMESTEP 131
+#define LM3633_TIME_OFFSET 61
+#define LM3633_PATTERN_REG_OFFSET 16
+#define LM3633_IMAX_OFFSET 6
+
+enum lm3633_led_bank_id {
+ LM3633_LED_BANK_C,
+ LM3633_LED_BANK_D,
+ LM3633_LED_BANK_E,
+ LM3633_LED_BANK_F,
+ LM3633_LED_BANK_G,
+ LM3633_LED_BANK_H,
+ LM3633_MAX_LEDS,
+};
+
+/**
+ * struct ti_lmu_led_chip
+ *
+ * @dev: Parent device pointer
+ * @lmu: LMU structure. Used for register R/W access.
+ * @lock: Secure handling for multiple user interface access
+ * @lmu_led: Multiple LED strings
Could you clarify what "string" means here?
+ * @num_leds: Number of LED strings
and here?
Oops! I forgot to replace this term with 'output channel'. Thanks for
catching this.
+static u8 lm3633_convert_time_to_index(unsigned int msec)
+{
+ u8 idx, offset;
+
+ /*
+ * Find an approximate index
I think that we shouldn't approximate but clamp the msec
to the nearest possible device setting.
+ *
+ * 0 <= time <= 1000 : 16ms step
+ * 1000 < time <= 9700 : 131ms step, base index is 61
+ */
+
+ msec = min_t(int, msec, LM3633_MAX_PERIOD);
+
+ if (msec <= 1000) {
+ idx = msec / LM3633_SHORT_TIMESTEP;
+ if (idx > 1)
+ idx--;
+ offset = 0;
+ } else {
+ idx = (msec - 1000) / LM3633_LONG_TIMESTEP;
+ offset = LM3633_TIME_OFFSET;
+ }
+
+ return idx + offset;
+}
+
+static u8 lm3633_convert_ramp_to_index(unsigned int msec)
+{
+ const int ramp_table[] = { 2, 250, 500, 1000, 2000, 4000, 8000, 16000 };
+ int size = ARRAY_SIZE(ramp_table);
+ int i;
+
+ if (msec <= ramp_table[0])
+ return 0;
+
+ if (msec > ramp_table[size - 1])
+ return size - 1;
+
+ for (i = 1; i < size; i++) {
+ if (msec == ramp_table[i])
+ return i;
+
+ /* Find an approximate index by looking up the table */
Similarly here. So you should have an array of the possible msec
values and iterate through it to look for the nearest one.
Driver uses 'ramp_table[]' for this purpose. Could you describe it in
more details?
+
+static int lm3633_led_brightness_set(struct led_classdev *cdev,
+ enum led_brightness brightness)
+{
+ struct ti_lmu_led *lmu_led = container_of(cdev, struct ti_lmu_led,
+ cdev);
+ struct ti_lmu_led_chip *chip = lmu_led->chip;
+ struct regmap *regmap = chip->lmu->regmap;
+ u8 reg = LM3633_REG_BRT_LVLED_BASE + lmu_led->bank_id;
+ int ret;
+
+ mutex_lock(&chip->lock);
+
+ ret = regmap_write(regmap, reg, brightness);
+ if (ret) {
+ mutex_unlock(&chip->lock);
+ return ret;
+ }
+
+ if (brightness == 0)
+ lm3633_led_disable_bank(lmu_led);
This should be checked at first, as I suppose that disabling
a bank suffices to turn the LED off.
Well, it's not a big deal when turn off the LED. However, our silicon
designer recommended brightness update should be done prior to enabling
LED bank. Let me share some block diagram.
[I2C logic] - [brightness control] - [control bank] - [output channel]
If control bank is enabled first, then previous brightness value in
register can be used instead of new updated brightness. So brightness
update should be done first.
+static u8 lm3633_led_scale_max_brightness(struct ti_lmu_led *lmu_led, u32 imax)
+{
+ u8 max_current = lm3633_led_convert_current_to_index(imax);
+ const u8 max_brightness_table[] = {
+ [LMU_IMAX_5mA] = 191,
+ [LMU_IMAX_6mA] = 197,
+ [LMU_IMAX_7mA] = 203,
+ [LMU_IMAX_8mA] = 208,
+ [LMU_IMAX_9mA] = 212,
+ [LMU_IMAX_10mA] = 216,
+ [LMU_IMAX_11mA] = 219,
+ [LMU_IMAX_12mA] = 222,
+ [LMU_IMAX_13mA] = 225,
+ [LMU_IMAX_14mA] = 228,
+ [LMU_IMAX_15mA] = 230,
+ [LMU_IMAX_16mA] = 233,
+ [LMU_IMAX_17mA] = 235,
+ [LMU_IMAX_18mA] = 237,
+ [LMU_IMAX_19mA] = 239,
+ [LMU_IMAX_20mA] = 241,
+ [LMU_IMAX_21mA] = 242,
+ [LMU_IMAX_22mA] = 244,
+ [LMU_IMAX_23mA] = 246,
+ [LMU_IMAX_24mA] = 247,
+ [LMU_IMAX_25mA] = 249,
+ [LMU_IMAX_26mA] = 250,
+ [LMU_IMAX_27mA] = 251,
+ [LMU_IMAX_28mA] = 253,
+ [LMU_IMAX_29mA] = 254,
+ [LMU_IMAX_30mA] = 255,
+ };
After analyzing the subject one more time I think that we need to
change the approach regarding max brightness issue.
At first - we shouldn't fix max current to max possible register value.
Instead we should take led-max-microamp property and write its value
to the [0x22 + bank offset] registers.
With this approach whole 0-255 range of brightness levels will be
valid for the driver.
In effect all LMU_IMAX* enums seem to be not needed.
Good to hear that, it's the most simplest work for the device ;)
Let me update the driver. Thanks!
Best regards,
Milo
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