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

[Serge Semin]

Hi Geert

On Tue, Jun 21, 2022 at 09:03:25AM +0200, Geert Uytterhoeven wrote:
> Hi Serge,
> 
> On Mon, Jun 20, 2022 at 10:56 PM Serge Semin <fancer.lancer at gmail.com> wrote:
> > On Sat, Jun 18, 2022 at 01:30:28PM +0100, Conor Dooley wrote:
> > > From: Conor Dooley <conor.dooley at microchip.com>
> > >

[...]

> > > +
> > > +        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.

Can't argue with that.) My note regarding the current DW APB SSI
driver was mainly addressed for the Canaan K210 users, since
should the SoC-based board really have the Quad Tx/Rx SPI bus
most likely the interface won't work with the full bandwidth.
So it is a good reason to perform the platform research and if
possible alter the driver accordingly.

-Sergey

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
> 
> 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