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[0/3] leds: add driver for SPI driven WorldSemi WS2812B RGB LEDs

Message ID 20221129140955.137361-1-gch981213@gmail.com
Headers show
Series leds: add driver for SPI driven WorldSemi WS2812B RGB LEDs | expand

Message

Chuanhong Guo Nov. 29, 2022, 2:09 p.m. UTC 
This patch adds support for driving a chain of WS2812B LED chips
using SPI bus.

WorldSemi WS2812B is a individually addressable LED chip that
can be chained together and controlled individually using a
single wire. The chip recognize a long pulse as a bit of 1 and
a short pulse as a bit of 0. Host sends a continuous stream
of 24-bits color values, each LED chip takes the first 3 byte
it receives as its color value and passes the leftover bytes to
the next LED on the chain.

This driver simulates this protocol using SPI bus by sending
a long pulse as 3'b110 and a short pulse as 3'b100. The SPI
frequency needs to be 2.105MHz~2.85MHz for the timing to be
correct and the controller needs to transfer all the bytes
continuously.

Chuanhong Guo (3):
  dt-bindings: vendor-prefixes: add an entry for WorldSemi
  dt-bindings: leds: add dt schema for worldsemi,ws2812b-spi
  leds: add driver for SPI driven WorldSemi WS2812B RGB LEDs

 .../bindings/leds/worldsemi,ws2812b-spi.yaml  | 131 +++++++++++
 .../devicetree/bindings/vendor-prefixes.yaml  |   2 +
 drivers/leds/rgb/Kconfig                      |  11 +
 drivers/leds/rgb/Makefile                     |   1 +
 drivers/leds/rgb/leds-ws2812b-spi.c           | 222 ++++++++++++++++++
 5 files changed, 367 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/leds/worldsemi,ws2812b-spi.yaml
 create mode 100644 drivers/leds/rgb/leds-ws2812b-spi.c

Comments

Chuanhong Guo Dec. 1, 2022, 12:41 p.m. UTC | #1 
Hi!

On Wed, Nov 30, 2022 at 7:59 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
> >> [...]
> >> So this is brightness of each color...
> >
> > I don't think so.
> > See the kernel doc for multicolor LED:
> > https://docs.kernel.org/leds/leds-class-multicolor.html
> > This property sets the sysfs file multi_intensity while the
> > actual LED brightness is controlled with another sysfs
> > file called 'brightness'.
> > Setting multi_intensity alone doesn't change the LED
> > brightness at all.
>
> If you had brightness, that would be correct. But you do not have
> brightness, right?

The brightness can be set using sysfs, but I didn't implement a
default brightness in my driver.
My original intent for this property is to set a default color for legacy
led softwares which can only control the brightness and doesn't
support setting the color value yet.

> Therefore the final brightness is always:
>
> subled[i].brightness = 255 * subled[i].intensity / max_brightness (also
> 255);
>
> Or your bindings are incomplete...

I do agree that adding a default-brightness will make this more
useful. I'll add this feature in the next version.