Re: [PATCH v2 06/13] leds: st1202: Scale pattern brightness to the 12-bit PWM range

[sashiko-bot@kernel.org]

> The LED1202 PWM registers are 12 bits wide, but st1202_led_pattern_set()
> writes the 8-bit brightness value carried by struct led_pattern into
> them unscaled. A pattern step asking for full brightness therefore
> drives the channel at 255 out of 4095, about 6% duty cycle, so a pattern
> is dimmer than the same brightness set directly.
> 
> Scale the value to the full PWM range before programming it.
> 
> Scale against max_brightness rather than the register maximum. The LED
> core takes max_brightness from the DT max-brightness property, so a
> board can declare a ceiling below full scale, and the pattern trigger
> already rejects steps above it. Scaling against a hardcoded 255 would
> leave such a board unable to reach its own declared maximum from the
> pattern path while the brightness path reaches it.
> 
> Scaling divides by max_brightness. The LED core replaces a zero
> max-brightness from the device tree with LED_FULL, so the divisor should
> never be zero, but the helper returns zero rather than rely on that.
> max_brightness is capped at U8_MAX, the driver's own maximum, so a
> device tree declaring more than the part supports is treated as full
> scale. struct led_pattern brightness is signed, so clamp both ends and
> floor a negative value to LED_OFF rather than let it wrap.
> 
> Document that a step is relative to max_brightness, since the range
> given in the documentation no longer holds when the device tree sets
> max-brightness.
> 
> Fixes: 259230378c65 ("leds: Add LED1202 I2C driver")
> Signed-off-by: Manuel Fombuena <fombuena@outlook.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/GV1PR08MB8497668D389D43F680D2CE3CC5BA2@GV1PR08MB8497.eurprd08.prod.outlook.com?part=6