linux-kernel - Re: [PATCH v8 2/2] leds: sc27xx: Add pattern_set/clear interfaces for LED controller

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Date:   Wed, 5 Sep 2018 14:52:47 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Pavel Machek <pavel@....cz>, rteysseyre@...il.com,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 2/2] leds: sc27xx: Add pattern_set/clear interfaces for
 LED controller

On 5 September 2018 at 10:43, Baolin Wang <baolin.wang@...aro.org> wrote:
> Hi Jacek,
>
> On 5 September 2018 at 04:19, Jacek Anaszewski
> <jacek.anaszewski@...il.com> wrote:
>> Hi Baolin,
>>
>> On 09/04/2018 01:01 PM, Baolin Wang wrote:
>>> This patch implements the 'pattern_set'and 'pattern_clear'
>>> interfaces to support SC27XX LED breathing mode.
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>> ---
>>> Changes from v7:
>>>  - Add its own ABI documentation file.
>>>
>>> Changes from v6:
>>>  - None.
>>>
>>> Changes from v5:
>>>  - None.
>>>
>>> Changes from v4:
>>>  - None.
>>>
>>> Changes from v3:
>>>  - None.
>>>
>>> Changes from v2:
>>>  - None.
>>>
>>> Changes from v1:
>>>  - Remove pattern_get interface.
>>> ---
>>>  .../ABI/testing/sysfs-class-led-driver-sc27xx      |   11 +++
>>>  drivers/leds/leds-sc27xx-bltc.c                    |   94 ++++++++++++++++++++
>>>  2 files changed, 105 insertions(+)
>>>  create mode 100644 Documentation/ABI/testing/sysfs-class-led-driver-sc27xx
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-class-led-driver-sc27xx b/Documentation/ABI/testing/sysfs-class-led-driver-sc27xx
>>> new file mode 100644
>>> index 0000000..ecef3ba
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-class-led-driver-sc27xx
>>> @@ -0,0 +1,11 @@
>>> +What:                /sys/class/leds/<led>/hw_pattern
>>> +Date:                September 2018
>>> +KernelVersion:       4.20
>>> +Description:
>>> +             Specify a hardware pattern for the SC27XX LED. For the SC27XX
>>> +             LED controller, it only supports 4 hardware patterns to configure
>>
>> If I understand it correctly then the four components: low, rise, high,
>> and fall time make a single pattern. So calling it "4 hardware patterns"
>> can be misleading. Below you're using "stage" notion - it would be good
>> to use it consequently on the whole span of this document.
>
> Sure. I will modify the documentation to avoid misleading words.
>
>>
>>> +             the low time, rise time, high time and fall time for the breathing
>>> +             mode, and each stage duration unit is 125ms. So the format of
>>> +             the hardware pattern values should be:
>>
>> I'd be more precise here:
>>
>> Min stage duration: ???
>> Max stage duration: ???
>> Stage duration step: 125 ms
>
> OK.
>
>>
>>> +             "brightness_1 duration_1 brightness_2 duration_2 brightness_3
>>> +             duration_3 brightness_4 duration_4".
>>
>> Looking at sc27xx_led_pattern_set() it doesn't seem like you would
>> use brightnesses other then brightness_1. I assume that the low
>> brightness is fixed to 0 and the high brightness is the brightness_1.
>> If yes, than we don't need brightnesses in this pattern definition,
>> since the current brightness will suffice.
>>
>> You'd need to alter the hw_pattern description to say that the
>> brightness currently set is to be used as a high brightness, and the
>> hw_pattern for this driver consists only of the four delta_t components.
>
> Sorry for confusing here. For SC27XX LED, the 4 stages use one same
> brightness. To be compatible with the hardware pattern format, so we
> force to set one brightness for each stage. I will add some comments
> to explain the LED expects the same brightness for each stage instead
> of using the current brightness file which is not used for our
> breathing mode.
>
>>
>> This is clear example of what I had on mind when having doubts
>> about using tuples for pattern_set.
>>
>> Alternatively, if we want to enforce tuples format for hw_pattern,
>> and if we want to be consistent - we'd need to require defining target
>> brightness for each stage properly, i.e.
>>
>> echo "100 500 100 500 0 500 0 500" > pattern

After more thinking, I will change the description to reflect the real
brightness according to your suggestion. Please see my new patch.
Thanks.

>>
>> Which would mean:
>>
>> 1. Rise from brightness 0 to 100 for 500 ms.
>> 2. Keep brightness 100 for 500 ms.
>> 3. Fall from brightness 100 to 0 for 500 ms.
>> 4. Keep brightness 0 for 500 ms.
>>
>> --
>> Best regards,
>> Jacek Anaszewski
>
>
>
> --
> Baolin Wang
> Best Regards



-- 
Baolin Wang
Best Regards