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

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Date:   Tue, 4 Sep 2018 22:19:43 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Baolin Wang <baolin.wang@...aro.org>, pavel@....cz
Cc:     rteysseyre@...il.com, bjorn.andersson@...aro.org,
        broonie@...nel.org, linus.walleij@...aro.org,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/2] leds: sc27xx: Add pattern_set/clear interfaces for
 LED controller

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.

> +		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

> +		"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.

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

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