leds: st1202: Fix pattern duration prescaler and pattern_clear skip marker

The PATy_DUR register encodes duration as N × 22.2 ms, with register
value 0 reserved as a pattern skip indicator (§7.10). The driver
incorrectly subtracted 1 from the register value:

  value / ST1202_MILLIS_PATTERN_DUR_MIN - 1

This caused two problems:

  - All programmed durations were off by one step (~22 ms too short).
  - Writing the minimum duration (22 ms) produced register value 0,
    silently skipping the pattern step instead of setting a 22 ms
    duration.

The maximum duration constant was also wrong at 5660 ms. The 8-bit
register saturates at 255, giving a maximum of 5610 ms (22 ms × 255).
Values above 5653 ms were already producing a uint8_t overflow and
writing 0 to the hardware.

Fix the formula by removing the erroneous subtraction, and derive the
maximum from the register width so the relationship is explicit. Update
the documentation to reflect the correct maximum.

This exposes a secondary issue: pattern_clear() was calling
st1202_duration_pattern_write() with ST1202_MILLIS_PATTERN_DUR_MIN to
reset unused slots, accidentally relying on the broken formula to
produce register value 0. With the corrected formula, the same call
writes 0x01 (22 ms), leaving unused slots as valid 22 ms zero-PWM
steps and making the LED appear off for 7 × 22 ms out of every cycle.

Write 0 directly to the duration registers in pattern_clear() so unused
slots are always explicitly marked as skip, independently of the
conversion formula.

Fixes: 259230378c65 ("leds: Add LED1202 I2C driver")
Signed-off-by: Manuel Fombuena <fombuena@outlook.com>
Assisted-by: Claude:claude-sonnet-4-6
Link: https://patch.msgid.link/GV1PR08MB84971D3AF982F4F707A378F0C5F52@GV1PR08MB8497.eurprd08.prod.outlook.com
Signed-off-by: Lee Jones <lee@kernel.org>

0 files changed, 0 insertions, 0 deletions