On 06/06/2022 03:39, ChiYuan Huang wrote:

Krzysztof Kozlowski [off-list ref] 於 2022年6月6日 週一 上午12:11寫道：

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On 02/06/2022 17:31, ChiYuan Huang wrote:

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Krzysztof Kozlowski [off-list ref] 於 2022年6月2日 週四 下午9:58寫道：

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On 02/06/2022 15:56, Rob Herring wrote:

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On Thu, May 26, 2022 at 12:32:12PM +0200, Krzysztof Kozlowski wrote:

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On 26/05/2022 10:13, ChiYuan Huang wrote:

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Krzysztof Kozlowski [off-list ref] 於 2022年5月26日 週四 下午4:06寫道：

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On 26/05/2022 05:16, cy_huang wrote:

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From: ChiYuan Huang <redacted>

Add the new property for ocp level selection.

Signed-off-by: ChiYuan Huang <redacted>
---
 .../bindings/leds/backlight/richtek,rt4831-backlight.yaml         | 8 ++++++++
 include/dt-bindings/leds/rt4831-backlight.h                       | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/richtek,rt4831-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/richtek,rt4831-backlight.yaml
index e0ac686..c1c59de 100644
--- a/Documentation/devicetree/bindings/leds/backlight/richtek,rt4831-backlight.yaml
+++ b/Documentation/devicetree/bindings/leds/backlight/richtek,rt4831-backlight.yaml

@@ -47,6 +47,14 @@ properties:
     minimum: 0
     maximum: 3

+  richtek,bled-ocp-sel:

Skip "sel" as it is a shortcut of selection. Name instead:
"richtek,backlight-ocp"

OK, if so, do I need to rename all properties from 'bled' to 'backlight' ?
If  only this property is naming as 'backlight'. it may conflict with
the others like as "richtek,bled-ovp-sel".

Ah, no, no need.

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+    description: |
+      Backlight OCP level selection, currently support 0.9A/1.2A/1.5A/1.8A

Could you explain here what is OCP (unfold the acronym)?

Yes. And the full name is 'over current protection'.

Thanks and this leads to second thing - you encode register value
instead of logical value. This must be a logical value in mA, so
"richtek,bled-ocp-microamp".

We already have common properties for setting current of LEDs. We should
use that here I think.

It might not be exactly the same. We have "led-max-microamp" which is
the maximum allowed current. I guess over-current protection level  is
slightly higher (e.g. led-max-microamp + 1). IOW, led-max-microamp is
something which still can be set and used by system/hardware. OCP should
not.

Yap, you're right.

So I am right or Rob?

As I know, both are incorrect.

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From the modern backlight IC design, it uses the boost converter architecture.
This OCP level is to limit the inductor current when the internal MOS
switch turn on.
Details can refer to the below wiki link
https://en.wikipedia.org/wiki/Boost_converter

And based on it, OVP is used to limit the inductor output voltage.
Each channel maximum current is based on the IC affordable limit.
It is more like as what you said 'led-max-microamp'.

So boost voltage level may depend on the LED VF.
The different series of LED may cause different boost voltage.

RT4831's OVP/OCP is not just the protection, more like as the limit.

This suggests Rob is right, so let's use led-max-microamp property?

No, the meaning is different. 'led-max-microamp' always means the
channel output current.
It already can be adjusted by backlight brightness node.

For example
low voltage side (3.3~4.4V) to generate the boost voltage to 16~17V,
even 20V for BLED Vout.
This OCP is to limit the input current of low voltage side.

After the explanation, do you still think it's the same thing?

This sounds differently so I propose to use this dedicated property with
the changes I asked for.


Best regards,
Krzysztof