linux-kernel - Re: [PATCH v5 1/2] dt: bindings: lm3601x: Introduce the lm3601x driver

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Date:   Fri, 11 May 2018 07:12:39 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>
CC:     <robh+dt@...nel.org>, <mark.rutland@....com>, <afd@...com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-leds@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] dt: bindings: lm3601x: Introduce the lm3601x
 driver

Jacek

Thanks for the review

On 05/10/2018 03:17 PM, Jacek Anaszewski wrote:
> Hi Dan,
> 
> On 05/10/2018 09:10 PM, Dan Murphy wrote:
>> On 05/10/2018 02:06 PM, Dan Murphy wrote:
>>> Pavel
>>>
>>> On 05/10/2018 01:54 PM, Pavel Machek wrote:
>>>> Hi!
>>>>
>>>>> Introduce the device tree bindings for the lm3601x
>>>>> family of LED torch, flash and IR drivers.
>>>>>
>>>>> Signed-off-by: Dan Murphy <dmurphy@...com>
>>>>
>>>> Better, thanks.
>>>>> +++ b/Documentation/devicetree/bindings/leds/leds-lm3601x.txt
>>>>> @@ -0,0 +1,50 @@
>>>>> +* Texas Instruments - lm3601x Single-LED Flash Driver
>>>>
>>>> Ok, so is it single-LED driver, or can it driver ir & white LEDs at
>>>> the same time?
>>>
>>> It is a single LED driver.  It can drive a Torch white LED or IR LED indefinitely or if the driver
>>> is programmed to strobe mode the driver will drive the configured LED for the flash timeout specified.
>>>
>>> Basically a flash and a flash light. IR or White LED.
>>>
>>>
>>>>
>>>>> +Example:
>>>>> +led-controller@64 {
>>>>> +    compatible = "ti,lm36010";
>>>>> +    #address-cells = <1>;
>>>>> +    #size-cells = <0>;
>>>>> +    reg = <0x64>;
>>>>> +
>>>>> +    led@0 {
>>>>> +        reg = <0>;
>>>>> +        label = "white:torch";
>>>>> +        led-max-microamp = <10000>;
>>>>> +    };
>>>>> +
>>>>> +    led@1 {
>>>>> +        reg = <1>;
>>>>> +        label = "white:flash";
>>>>> +        flash-max-microamp = <10000>;
>>>>> +        flash-max-timeout-us = <800>;
>>>>> +    };
>>>>
>>>> Is this realistic config? I'd expect flash to use more power than
>>>> torch, and would expect longer timeout than 0.8msec.
>>>
>>> Timeout in the spreadsheet is ms I will update this example and code
>>> Current in the spreadsheet is mA I will update this example and code
>>>
>>>>
>>>> Also.. if this is physically one white LED, it should not be
>>>> spread over reg = <0> and reg = <1>...
>>>
>>> If the torch LED and strobe LED are the same LED how do I expose them both to the user.
>>> It is up to consumer to configure the required interfaces they want to expose to the filesystem.
> 
> LED flash class interface is prepared for it.
> led_clasdev_flash_register() internally calls led_classdev_register(),
> so there is brightness file available for torch related operations.

Yes the flash class may handle this and expose the brightness node but the HW has two different registers to set the
corresponding brightness so one set brightness node does not work.
There is no way to differentiate between the strobe brightness (register 4) and the torch brightness (register 3).

When the enable register is written the driver will read the corresponding register and set
the current for the LED.

This is why I separated out the strobe from the torch into 2 different LED nodes.

I cannot seem to find the data sheet on line for the max77693 so I cannot verify that the device only has
a single brightness register for both torch and strobe.


> 
>>> Maybe they don't want the strobe feature and just want LED on/off and switch between IR and White.
>>>
>>> The IR is driven via a different output pin.
>>
>> Correction.  There is only one LED drive pin.  The mode selected determines how the device will drive the
>> LED.  So you may have one device to drive a Torch and another device to drive the LED.
> 
> But only one type of LED can be soldered on the board at a time, right?
> If yes, then this is clearly a DT related configuration, and only
> one child DT node should be defined for given board.

But see above.  There is not a clean way to expose the torch/ir and strobe separately.

Dan


> 
>> Strobe is available in either case but not always required if strobe is not desired by the customer hence
>> why I have a separate DT node for it.
>>
>> Dan
>>
>>>
>>> Dan
>>>
>>>>
>>>> Best regards,
>>>>                                     Pavel
>>>>
>>>
>>>
>>
>>
> 


-- 
------------------
Dan Murphy