Re: [PATCH 1/2] spi: renesas,rzv2m-csi: Add SPI Slave related properties

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Mark,

On Wed, Sep 27, 2023 at 11:00 AM Mark Brown <broonie@xxxxxxxxxx> wrote:
> On Wed, Sep 27, 2023 at 09:59:05AM +0200, Geert Uytterhoeven wrote:
> > On Tue, Sep 26, 2023 at 11:08 PM Fabrizio Castro
> > > +    type: boolean
> > > +    description:
> > > +      Use CSI Slave Selection (SS) pin to enable transmission and reception when
> > > +      in slave mode.
>
> > Can't this be done in a more generic way? I had expected that the
> > existing SPI_NO_CS flag can be set using a property in the "slave" subnode,
> > but apparently there is no "spi-no-cs" property defined yet.
>
> The description is clearly saying there is a chip select, _NO_CS seems
> entirely inappropriate.  It's not specified in the device tree because
> when there's no chip select for a device it's a fundamental property of
> how the device is controlled and we don't need any information beyond
> the compatible.

In host mode, it indeed doesn't matter, as you can have only a single
device connected with SPI_NO_CS.
In device mode, the device needs to know if it must monitor the chip
select line or not.

In hindsight, I should have kept the question I had written initially,
but deleted after having read the documentation for the corresponding
RZ/V2M register bits:

    What does it mean if this is false? That there is no chip select?

So "spi-no-cs" would be the inverse of "renesas,csi-ss".

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