Re: [PATCH 1/3] dt-bindings: leds: Add bindings for the TLC5925 controller

[Jean-Jacques Hiblot]

On 23/05/2022 17:30, Krzysztof Kozlowski wrote:
> On 23/05/2022 17:16, Jean-Jacques Hiblot wrote:
> > On 23/05/2022 12:14, Krzysztof Kozlowski wrote:
> > > On 23/05/2022 10:49, Jean-Jacques Hiblot wrote:
> > > > Add bindings documentation for the TLC5925 LED controller.
> > > >
> > > > Signed-off-by: Jean-Jacques Hiblot <jjhiblot@xxxxxxxxxxxxxxx>
> > > Thank you for your patch. There is something to discuss/improve.
> > >
> > > > ---
> > > > devicetree@xxxxxxxxxxxxxxx
> > > >    .../bindings/leds/leds-tlc5925.yaml           | 100 ++++++++++++++++++
> > > >    1 file changed, 100 insertions(+)
> > > >    create mode 100644 Documentation/devicetree/bindings/leds/leds-tlc5925.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/leds/leds-tlc5925.yaml b/Documentation/devicetree/bindings/leds/leds-tlc5925.yaml
> > > > new file mode 100644
> > > > index 000000000000..156db599d5a1
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/leds/leds-tlc5925.yaml
> > > Filename: vendor,device
> > > so "ti,tlc5925-leds.yaml" for example.
> > >
> > >
> > >
> > > > @@ -0,0 +1,100 @@
> > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/leds/leds-tlc5925.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: LEDs connected to TI TLC5925 controller
> > > > +
> > > > +maintainers:
> > > > +  - Jean-Jacques Hiblot <jjhiblot@xxxxxxxxxxxxxxx>
> > > > +
> > > > +description: |
> > > > +  The TLC5925 is a low-power 16-channel constant-current LED sink driver.
> > > > +  It is controlled through a SPI interface.
> > > > +  It is built around a shift register and latches which convert serial
> > > > +  input data into a parallel output. Several TLC5925 can be chained to
> > > > +  control more than 16 LEDs with a single chip-select.
> > > > +  The brightness level cannot be controlled, each LED is either on or off.
> > > > +
> > > > +  Each LED is represented as a sub-node of the ti,tlc5925 device.
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    const: ti,tlc5925
> > > > +
> > > > +  shift_register_length:
> > > > +    maxItems: 1
> > > No...
> > > 1. Did you test your bindings with dt_binding_check? This fails
> > > obviously... please, do not send untested bindings.
> > >
> > > 2. vendor prefix, no underscores, proper type, maxItems look wrong here
> > >
> > > > +    description: |
> > > > +      The length of the shift register. If several TLC5925 are chained,
> > > > +      shift_register_length should be set to 16 times the number of TLC5925.
> > > > +      The value must be a multiple of 8.
> > > > +
> > > > +  "#address-cells":
> > > > +    const: 1
> > > > +
> > > > +  "#size-cells":
> > > > +    const: 0
> > > > +
> > > > +  output-enable-b-gpios:
> > > > +    description: |
> > > > +      GPIO pins to enable/disable the parallel output. They describe the GPIOs
> > > > +      connected to the OE/ pin of the TLC5925s.
> > > maxItems
> > There is no limitation in the driver itself. The actual number of items
> > here really depends on the number of chips and how they are wired.
> So you could daisy chain 4 billion of devices? Because by not using any
> limit you claim that 4 billion is doable?

You could chain 1000 devices or more and have 16000 leds. It would be a 
bit tedious to describe them all in the DTS though.

We can impose a limit but it will be arbitrary. Is this how it is 
usually treated ?

> > > > +
> > > > +patternProperties:
> > > > +  "@[a-f0-9]+$":
> > > How many LEDs you can have here? Usually it is limited, so the pattern
> > > should be narrowed.
> > There is no limitation here either. The chips can be chained to augment
> > the number of LEDs.
> >
> > The max number of LED is equal to the length of the shift-register.
>
>
> Best regards,
> Krzysztof