Date:   Tue, 25 Sep 2018 19:15:31 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Pavel Machek <pavel@....cz>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        rteysseyre@...il.com, 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 v12 1/2] leds: core: Introduce LED pattern trigger

On 23 September 2018 at 20:25, Jacek Anaszewski
<jacek.anaszewski@...il.com> wrote:
> On 09/22/2018 09:44 PM, Pavel Machek wrote:
>> On Sat 2018-09-22 00:18:13, Pavel Machek wrote:
>>> On Sat 2018-09-22 00:11:29, Jacek Anaszewski wrote:
>>>> On 09/21/2018 11:17 PM, Pavel Machek wrote:
>>>>> On Fri 2018-09-21 22:59:40, Jacek Anaszewski wrote:
>>>>>> Hi Baolin,
>>>>>>
>>>>>> On 09/21/2018 05:31 AM, Baolin Wang wrote:
>>>>>>> Hi Jacek and Pavel,
>>>>>>>
>>>>>>> On 11 September 2018 at 10:47, Baolin Wang <baolin.wang@...aro.org> wrote:
>>>>>>>> This patch adds one new led trigger that LED device can configure
>>>>>>>> the software or hardware pattern and trigger it.
>>>>>>>>
>>>>>>>> Consumers can write 'pattern' file to enable the software pattern
>>>>>>>> which alters the brightness for the specified duration with one
>>>>>>>> software timer.
>>>>>>>>
>>>>>>>> Moreover consumers can write 'hw_pattern' file to enable the hardware
>>>>>>>> pattern for some LED controllers which can autonomously control
>>>>>>>> brightness over time, according to some preprogrammed hardware
>>>>>>>> patterns.
>>>>>>>>
>>>>>>>> Signed-off-by: Raphael Teysseyre <rteysseyre@...il.com>
>>>>>>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>>>>
>>>>>>> Do you have any comments for the v12 patch set? Thanks.
>>>>>>
>>>>>> We will probably have to remove hw_pattern from ledtrig-pattern
>>>>>> since we are unable to come up with generic interface for it.
>>>>>> Unless thread [0] will end up with some brilliant ideas. So far
>>>>>> we're waiting for Pavel's reply.
>>>>>>
>>>>>> [0] https://lkml.org/lkml/2018/9/13/1216
>>>>>
>>>>> To paint a picture:
>>>>>
>>>>> brightness
>>>>>
>>>>>    rise hold          lower       hold down
>>>>>   ^    XXXXXXXXXXXXXXX
>>>>>   |   X               XX
>>>>>   |  X                  XX
>>>>>   | X                     XXXXXXXXXXXXXXXXXXXXXXXXXX
>>>>>   +-------------------------------------------------------> time
>>>>>
>>>>> This is what Baolin's hardware can do, right?
>>>>>
>>>>> This is also what pattern trigger can do, right?
>>>>>
>>>>> So all we need to do is match the two interfaces, so that hw_pattern
>>>>> returns -EINVAL on patterns hardware can not actually do.
>>>>>
>>>>> I believe I described code to do that in [0] above.
>>>>
>>>> You said that we should get the same effect by writing the
>>>> same series of tuples to either pattern or hw_pattern file.
>>>>
>>>> Below command consists of four tuples (marked with brackets
>>>> to highlight), and it will activate breathing mode in Baolin's
>>>> hw_pattern:
>>>>
>>>> "[0 rise_duration] [brightness high_duration] [brightness fall_duration]
>>>> [0   low_duration]"
>>>>
>>>> Now, I can't see how these four tuples could force the software
>>>> fallback to produce breathing effect you depicted.
>>>
>>> I really should get some sleep now. But my intention was that software
>>> fallback produces just that with those four tuples. (If it does not,
>>> we can fix the software fallback to do just that).
>>
>> And you are right, v12 1/2 seems to do the wrong thing.
>>
>> My "brilliant idea" is to something closer to the original version I
>> posted here. I'm attaching it for reference.
>>
>> I'm also attaching the original documentation. It was clearly designed
>> to do smooth transitions, too. (But pattern is written in slightly
>> different way there, AFAICT).
>>
>> Clearly, having same semantics for pattern and hw_pattern is possible.
>
> Thank you for the attachment. The documentation part makes everything
> clear. Comparing the patch from the attachment and the Baolin's patch
> there is one vital part missing, from the original
> pattern_trig_update():
>
> if (data->next->brightness == data->curr->brightness) {
> [...]
> } else {
>         /* Gradual dimming */
>         led_set_brightness(data->led_cdev, compute_brightness(data));
>         data->delta_t += UPDATE_INTERVAL;
>         mod_timer(&data->timer, jiffies
>                 + msecs_to_jiffies(UPDATE_INTERVAL));
> }

I have some confusions about this, if data->next->brightness !=
data->curr->brightness, we should always do gradual dimming? But
suppose below pattan values:
echo "0 100 20 100 40 100 80 100 100 100" > pattern

I do not want to do gradual dimming, just change the brightness with duration.

> And the compute_brightness() implementation:
>
> static int compute_brightness(struct pattern_trig_data *data)
> {
>         if (data->delta_t == 0)
>                 return data->curr->brightness;
>
>         if (data->curr->delta_t == 0)
>                 return data->next->brightness;
>
>         return data->curr->brightness + data->delta_t
>                 * (data->next->brightness - data->curr->brightness)
>                 / data->curr->delta_t;
> }
>
> With the above the linear gradual dimming is indeed feasible.
> And for non-linear dimming like breathing mode the hw_pattern will do.

I am still not sure when we need the linear gradual dimming? When
failed to set hardware pattern?

>
> There is also vital discrepancy between the documentation and the
> proposed ledtrig-pattern implementation. The doc says:
>
> "Duration of 0 means brightness should immediately change to new value"

OK. Will add in next version.

>
> This syntax seems to be not supported in the Baolin's patch.
>
> With all the above covered we will be almost there.
>
> Now, only the issues raised by Bjorn need a clarification:
>
> On 09/08/2018 07:02 AM, Bjorn Andersson wrote:
> [...]
>> The controls for my hardware is:
>> * a list of brightness values
>> * the rate of the pattern
>
> The two can be described using [brightness delta_t] tuples.
>
>> * a flag to indicate that the pattern should be played from start
>>   to end, end to start or start to end to start
>
> As above, but the tuples would have to be suitably arranged.
>
> We won't need any specific flag to indicate how the pattern
> should be played, but instead explicitly give the tuples in the
> required order. For the start-end-start case the sequence of tuples
> will need to be tripled, but the middle part should be put in the
> reverse order.
>
>> * a boolean indicating if the pattern should be played once or repeated
>>   indefinitely.
>
> We will have "repeat" file for that.
>
> Baolin, would you mind adding the support for gradual dimming to your
> ledtrig-timer.c implementation?

Yes, I will do. Thanks.

-- 
Baolin Wang
Best Regards

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