Re: [PATCH 06/14] spi: dt-bindings: dw-apb-ssi: update spi-{r,t}x-bus-width for dwc-ssi

[Geert Uytterhoeven]

Hi Serge,

On Mon, Jun 20, 2022 at 10:56 PM Serge Semin <fancer.lancer@xxxxxxxxx> wrote:
> On Sat, Jun 18, 2022 at 01:30:28PM +0100, Conor Dooley wrote:
> > From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> >
> > snps,dwc-ssi-1.01a has a single user - the Canaan k210, which uses a
> > width of 4 for spi-{r,t}x-bus-width. Update the binding to reflect
> > this.
> >
> > Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > ---
> >  .../bindings/spi/snps,dw-apb-ssi.yaml         | 48 ++++++++++++++-----
> >  1 file changed, 35 insertions(+), 13 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml b/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml
> > index e25d44c218f2..f2b9e3f062cd 100644
> > --- a/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml
> > +++ b/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml
> > @@ -135,19 +135,41 @@ properties:
> >        of the designware controller, and the upper limit is also subject to
> >        controller configuration.
> >
> > -patternProperties:
> > -  "^.*@[0-9a-f]+$":
> > -    type: object
> > -    properties:
> > -      reg:
> > -        minimum: 0
> > -        maximum: 3
> > -
> > -      spi-rx-bus-width:
> > -        const: 1
> > -
> > -      spi-tx-bus-width:
> > -        const: 1
> > +if:
> > +  properties:
> > +    compatible:
> > +      contains:
> > +        const: snps,dwc-ssi-1.01a
> > +
> > +then:
> > +  patternProperties:
> > +    "^.*@[0-9a-f]+$":
> > +      type: object
> > +      properties:
> > +        reg:
> > +          minimum: 0
> > +          maximum: 3
> > +
> > +        spi-rx-bus-width:
> > +          const: 4
> > +
> > +        spi-tx-bus-width:
> > +          const: 4
> > +
> > +else:
> > +  patternProperties:
> > +    "^.*@[0-9a-f]+$":
> > +      type: object
> > +      properties:
> > +        reg:
> > +          minimum: 0
> > +          maximum: 3
> > +
> > +        spi-rx-bus-width:
> > +          const: 1
> > +
> > +        spi-tx-bus-width:
> > +          const: 1
>
> You can just use a more relaxed constraint "enum: [1 2 4 8]" here
> irrespective from the compatible string. The modern DW APB SSI
> controllers of v.4.* and newer also support the enhanced SPI Modes too
> (Dual, Quad and Octal). Since the IP-core version is auto-detected at
> run-time there is no way to create a DT-schema correctly constraining
> the Rx/Tx SPI bus widths. So let's keep the
> compatible-string-independent "patternProperties" here but just extend
> the set of acceptable "spi-rx-bus-width" and "spi-tx-bus-width"
> properties values.
>
> Note the DW APB SSI/AHB SSI driver currently doesn't support the
> enhanced SPI modes. So I am not sure whether the multi-lines Rx/Tx SPI
> bus indeed works for Canaan K210 AHB SSI controller. AFAICS from the
> DW APB SSI v4.01a manual the Enhanced SPI mode needs to be properly
> activated by means of the corresponding CSR. So most likely the DW AHB
> SSI controllers need some specific setups too.

That doesn't matter here, as DT describes hardware, not software
limitations.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds