[PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines

[Maxime Ripard]

On Sun, Jun 18, 2023 at 07:37:32PM +0200, Miquel Raynal wrote:
> Hello Maxime,
> 
> maxime at cerno.tech wrote on Sun, 18 Jun 2023 16:37:58 +0200:
> 
> > Hi,
> > 
> > On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote:
> > > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx
> > > data line at all. The operating system needs to know whether it can read
> > > registers from the device or not. Let's detail this specific design
> > > possibility by bounding the spi-rx-bus-width property.
> > > 
> > > Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
> > > ---
> > >  .../devicetree/bindings/display/panel/sitronix,st7789v.yaml   | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > index 0ccf0487fd8e..a25df7e1df88 100644
> > > --- a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > +++ b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > @@ -29,6 +29,10 @@ properties:
> > >    spi-cpha: true
> > >    spi-cpol: true
> > >  
> > > +  spi-rx-bus-width:
> > > +    minimum: 0
> > > +    maximum: 1
> > > +  
> > 
> > It's not clear to me what the default would be?
> 
> This binding references spi-peripheral-props.yaml which sets the
> default to 1, I believe it is sane to keep it that way?

I'm not sure.

The driver didn't need RX before, and we didn't have any property that
was expressing whether we had MISO in the device tree.

That means we had both devices with and without MISO expressed in the
same way, the driver handling both (by ignoring MISO entirely).

With this patch, you now introduce a property that specifies whether
MISO is connected or not, and defaults to MISO being there. And a later
patch will use MISO if it's available.

This means that, while it's working fine for devices that had MISO
connected, devices that didn't are assumed to have it, and the driver
makes use of it.

Maxime
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