Hi Florian,
On 06/22/2016 08:08 AM, Florian Vaussard wrote:
Hi Jacek,
Le 21. 06. 16 à 17:28, Jacek Anaszewski a écrit :
Hi Florian,
Thanks for the patch. I have two remarks below.
On 06/21/2016 09:29 AM, Florian Vaussard wrote:
Add device tree binding documentation for On Semiconductor NCP5623 I2C
LED driver. The driver can independently control the PWM of the 3
channels with 32 levels of intensity.
The current delivered by the current source can be controlled using the
led-max-microamp property. In order to control this value, it is also
necessary to know the current on the Iref pin, hence the
onnn,led-iref-microamp property. It is usually set using an external
bias resistor, following Iref = Vref/Rbias with Vref=0.6V.
Signed-off-by: Florian Vaussard <florian.vaussard@xxxxxxxxxx>
---
.../devicetree/bindings/leds/leds-ncp5623.txt | 44 ++++++++++++++++++++++
1 file changed, 44 insertions(+)
create mode 100644 Documentation/devicetree/bindings/leds/leds-ncp5623.txt
diff --git a/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
new file mode 100644
index 0000000..0dc8345
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
@@ -0,0 +1,44 @@
+* ON Semiconductor - NCP5623 3-Channel LED Driver
+
+The NCP5623 is a 3-channel I2C LED driver. The brightness of each
+channel can be independently set using 32 levels. Each LED is represented
+as a sub-node of the device.
+
+Required properties:
+ - compatible: Should be "onnn,ncp5623"
+ - reg: I2C slave address (fixed to 0x38)
+ - #address-cells: must be 1
+ - #size-cells: must be 0
+ - onnn,led-iref-microamp: Current on the Iref pin in microampere
I think that you don't need this property. Just provide the formula for
calculating led-max-microamp value, similarly as you're doing that in
the commit message.
I am not completely sure to understand your suggestion. So at the end, I have to
compute the value of the register (let call it 'ILED') that I need to send to
chip to configure the current source. The formula is:
ILED = 31 - 2400*Iref/led-max-microamp
led-max-microamp is the maximum current value for given LED.
According to the documentation it can be calculated as follows:
ILEDmax = Iref * 2400 / (31 - n)
Since this is global setting for all LEDs, then I'd always set n to 30,
and calculate max_brightness value for each LED separately, basing on
led-max-microamp property value. Effectively, I'm revoking my previous
statement about setting max_brightness to fixed level.
You can compare drivers/leds/leds-aat1290.c and its bindings, as it
uses similar approach.
I need two pieces of information that depends on the hardware setup; the current
on the Iref pin (which is setup by a bias resistor Iref = 0.6V/Rbias), and the
desired output current (usually limited due to the chosen LED or the required
brightness).
On the other hand, I could also simply ask people to put the right value of
'ILED' (between 0 - 31) directly in the device tree, but this is less user-friendly.
+ - led-max-microamp: Desired maximum current for each LED in microampere
+ (maximum 30000uA)
Please add instead of (maximum ...):
Valid values: min - max, step by N (rounded {up|down})
E.g.
Valid values: 10000 - 30000, step by 1000 (rounded down)
This is unfortunately not a linear relationship,
OK, please define only max and min value then.
led-max-microamp = 2400*Iref/(31-ILED)
thus steps are not constant. This can be seen on figure 5 (p.9) of the datasheet
[1].
Thanks for your review,
Florian
[1] http://www.onsemi.com/pub/Collateral/NCP5623-D.PDF
--
Best regards,
Jacek Anaszewski
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