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[188.155.176.92]) by smtp.gmail.com with ESMTPSA id n19-20020a05640205d300b0042de8155fa1sm8150758edx.0.2022.06.05.23.20.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 05 Jun 2022 23:20:23 -0700 (PDT) Message-ID: <5af6d6ff-c5e3-f764-fa9c-a2c3d7365082@linaro.org> Date: Mon, 6 Jun 2022 08:20:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH 1/2] dt-bindings: backlight: rt4831: Add the new property for ocp level selection Content-Language: en-US To: ChiYuan Huang Cc: Rob Herring , Krzysztof Kozlowski , Lee Jones , Daniel Thompson , Jingoo Han , Pavel Machek , Helge Deller , cy_huang , lucas_tsai@richtek.com, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , dri-devel , "open list:FRAMEBUFFER LAYER" , Linux LED Subsystem , lkml References: <1653534995-30794-1-git-send-email-u0084500@gmail.com> <1653534995-30794-2-git-send-email-u0084500@gmail.com> <1c7ab94c-a736-c629-bd8c-8a974803e2b9@linaro.org> <076d53d3-6062-686f-8e45-14c5f936bbf6@linaro.org> <20220602135604.GA2194286-robh@kernel.org> <12096a2c-98c3-9e77-785f-808cc3e1a0e4@linaro.org> From: Krzysztof Kozlowski In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 06/06/2022 03:39, ChiYuan Huang wrote: > Krzysztof Kozlowski 於 2022年6月6日 週一 上午12:11寫道： >> >> On 02/06/2022 17:31, ChiYuan Huang wrote: >>> Krzysztof Kozlowski 於 2022年6月2日 週四 下午9:58寫道： >>>> >>>> On 02/06/2022 15:56, Rob Herring wrote: >>>>> On Thu, May 26, 2022 at 12:32:12PM +0200, Krzysztof Kozlowski wrote: >>>>>> On 26/05/2022 10:13, ChiYuan Huang wrote: >>>>>>> Krzysztof Kozlowski 於 2022年5月26日 週四 下午4:06寫道： >>>>>>>> >>>>>>>> On 26/05/2022 05:16, cy_huang wrote: >>>>>>>>> From: ChiYuan Huang >>>>>>>>> >>>>>>>>> Add the new property for ocp level selection. >>>>>>>>> >>>>>>>>> Signed-off-by: ChiYuan Huang >>>>>>>>> --- >>>>>>>>> .../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. >>>>>> >>>>>>>> >>>>>>>>> + 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. >>> 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