Date:   Sun, 5 Apr 2020 11:31:06 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>, <pavel@....cz>
CC:     <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v19 04/18] leds: multicolor: Introduce a multicolor class
 definition


On 4/5/20 11:28 AM, Randy Dunlap wrote:
> On 4/5/20 9:18 AM, Dan Murphy wrote:
>> Jacek
>>
>> On 4/5/20 10:08 AM, Jacek Anaszewski wrote:
>>> Dan,
>>>
>>> On 4/3/20 4:39 PM, Dan Murphy wrote:
>>>> Randy
>>>>
>>>> Thanks for the review
>>>>
>>>> On 4/2/20 10:47 PM, Randy Dunlap wrote:
>>>>> Hi,
>>>>> Here are a few changes for you to consider:
>>>>>
>>>>> On 4/2/20 1:42 PM, Dan Murphy wrote:
>>>>>> Introduce a multicolor class that groups colored LEDs
>>>>>> within a LED node.
>>>>>>
>>>>>> The multi color class groups monochrome LEDs and allows controlling two
>>>>>         multicolor
>>>> Ack
>>>>>> aspects of the final combined color: hue and lightness. The former is
>>>>>> controlled via <color>_intensity files and the latter is controlled
>>>>>> via brightness file.
>>>>>>
>>>>>> Signed-off-by: Dan Murphy <dmurphy@...com>
>>>>>> ---
>>>>>> diff --git a/Documentation/leds/leds-class-multicolor.rst
>>>>>> b/Documentation/leds/leds-class-multicolor.rst
>>>>>> new file mode 100644
>>>>>> index 000000000000..5bb004999248
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/leds/leds-class-multicolor.rst
>>>>>> @@ -0,0 +1,95 @@
>>>>>> +====================================
>>>>>> +Multi Color LED handling under Linux
>>>>>      Multicolor
>>>> Ack
>>>>>> +====================================
>>>>>> +
>>>>>> +Description
>>>>>> +===========
>>>>>> +The multi color class groups monochrome LEDs and allows controlling two
>>>>>          multicolor
>>>> Ack
>>>>>> +aspects of the final combined color: hue and lightness. The former is
>>>>>> +controlled via the color_intensity array file and the latter is
>>>>>> controlled
>>>>>> +via brightness file.
>>>>>> +
>>>>>> +For more details on hue and lightness notions please refer to
>>>>>> +https://en.wikipedia.org/wiki/CIECAM02.
>>>>>> +
>>>>>> +Multicolor Class Control
>>>>>> +========================
>>>>>> +The multicolor class presents files that groups the colors as
>>>>>> indexes in an
>>>>>> +array.  These files are children under the LED parent node created
>>>>>> by the
>>>>>> +led_class framework.  The led_class framework is documented in
>>>>>> led-class.rst
>>>>>> +within this documentation directory.
>>>>>> +
>>>>>> +Each colored LED will be indexed under the color_* files. The order
>>>>>> of the
>>>>>> +colors are arbitrary the color_index file can be read to determine
>>>>>> the color
>>>>>> +to index value.
>>>>>> +
>>>>>> +The color_index file is an array that contains the string list of
>>>>>> the colors as
>>>>>> +they are defined in each color_* array file.
>>>>>> +
>>>>>> +The color_intensity is an array that can be read or written to for the
>>>>>> +individual color intensities.  All elements within this array must
>>>>>> be written in
>>>>>> +order for the color LED intensities to be updated.
>>>>>> +
>>>>>> +The color_max_intensity is an array that can be read to indicate
>>>>>> each color LED
>>>>>> +maximum intensity value.
>>>>>> +
>>>>>> +The num_color_leds file returns the total number of color LEDs that are
>>>>>> +presented in each color_* array.
>>>>>> +
>>>>>> +Directory Layout Example
>>>>>> +========================
>>>>>> +root:/sys/class/leds/multicolor:status# ls -lR
>>>>>> +-rw-r--r--    1 root     root          4096 Oct 19 16:16 brightness
>>>>>> +-r--r--r--    1 root     root          4096 Oct 19 16:16 color_index
>>>>>> +-rw-r--r--    1 root     root          4096 Oct 19 16:16
>>>>>> color_intensity
>>>>>> +-r--r--r--    1 root     root          4096 Oct 19 16:16 num_color_leds
>>>>>> +
>>>>>> +Multicolor Class Brightness Control
>>>>>> +===================================
>>>>>> +The multiclor class framework will calculate each monochrome LEDs
>>>>>> intensity.
>>>>>          multicolor
>>>> Ack
>>>>>> +
>>>>>> +The brightness level for each LED is calculated based on the color LED
>>>>>> +intensity setting divided by the parent max_brightness setting
>>>>>> multiplied by
>>>>>> +the requested brightness.
>>>>>> +
>>>>>> +led_brightness = brightness * color_intensity/max_brightness
>>>>>> +
>>>>>> +Example:
>>>>>> +A user first writes the color_intensity file with the brightness levels
>>>>>> +that for each LED that is necessary to achieve a blueish violet
>>>>>> output from a
>>>>> drop first "that".
>>>> Ack
>>>>>                        that are
>>>>> necessary                                   from an
>>>> Ack and NACK the "from an".  It is from a since R is a consonant
>>> But it sounds like a vowel and this rule for creating articles
>>> "applies to the sound of the letter beginning the word, not just the
>>> letter itself" [0].
>>>
>>> [0] https://www.grammar.com/a-vs-an-when-to-use/
>>>
>> We have had the same internal debate here at work.
>>
>> How does "Red" when you say it sound like a vowel?  It is definitely a "R" sound that is first not a vowel sound.
>>
>> To me "from an RGB" does not sound correct "from a RGB" is actually correct here because R or Red still leads with a consonant in both the sound and letter.
>>
>> If it sounds as if it is beginning with a vowel sound, *use an*.  Like in "an honor" as the h is silent here.  R is not silent in Red or RGB.
> It depends on how one reads "from a RGB." Do you say/think the letters R G B
> (I do), or do you think/say red-green-blue?
>
>  From the [0] web page:
>   Articles with Acronyms, a or an
>
> Finally, the rule applies to acronyms as well. If you pronounce a letter as a letter and it begins with a vowel sound, you should precede it with an. The consonants with vowel sounds include f, h, l, m, n, r, s, and x.
>
>      He flew in an SST. He fired an M‑1. He attended an FDA hearing.
>
> By the same token, if a vowel letter, with a consonant sound, is pronounced as a letter, you should use a.
>
>      He made a U‑turn.
>
> Got it? So what is your grade?
>
>      An A? A B? Surely not an F.
>
>
I will change it.  Its not that big of a change and not worth a 
continued debate

Dan

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