leds: qcom-lpg: Require pattern to follow documentation

The leds-trigger-pattern documentation describes how the brightness of
the LED should transition linearly from one brightness value to the
next, over the given delta_t.

But the pattern engine in the Qualcomm LPG hardware only supports
holding the brightness for each entry for the period.
This subset of patterns can be represented in the leds-trigger-pattern
by injecting zero-time transitions after each entry in the pattern,
resulting in a pattern that pattern that can be rendered by the LPG.

Rework LPG pattern interface to require these zero-time transitions, to
make it comply with this subset of patterns and reject the patterns it
can't render.

Fixes: 24e2d05d1b68 ("leds: Add driver for Qualcomm LPG")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

1 files changed, 5 insertions, 3 deletions

diff --git a/Documentation/leds/leds-qcom-lpg.rst b/Documentation/leds/leds-qcom-lpg.rst
index f12416f02dd8..de7ceead9337 100644
--- a/Documentation/leds/leds-qcom-lpg.rst
+++ b/Documentation/leds/leds-qcom-lpg.rst
@@ -35,11 +35,13 @@ Specify a hardware pattern for a Qualcomm LPG LED.
 The pattern is a series of brightness and hold-time pairs, with the hold-time
 expressed in milliseconds. The hold time is a property of the pattern and must
 therefor be identical for each element in the pattern (except for the pauses
-described below).
+described below). As the LPG hardware is not able to perform the linear
+transitions expected by the leds-trigger-pattern format, each entry in the
+pattern must be followed a zero-length entry of the same brightness.
 
 Simple pattern::
 
-    "255 500 0 500"
+    "255 500 255 0 0 500 0 0"
 
         ^
         |
@@ -54,7 +56,7 @@ in the pattern, the so called "low pause" and "high pause".
 
 Low-pause pattern::
 
-    "255 1000 0 500 255 500 0 500"
+    "255 1000 255 0 0 500 0 0 255 500 255 0 0 500 0 0"
 
         ^
         |