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SubjectRe: [PATCH v8 2/2] leds: sc27xx: Add pattern_set/clear interfaces for LED controller
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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@linaro.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

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