linux-kernel - Re: [PATCH v2 01/11] dt-bindings: spi: allow expressing DTR capability

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Message-ID: <CAMuHMdWMCDzQm0tjpybJZyHy4imbC9NqRXP5d4C0xgxQx-Pf8g@mail.gmail.com>
Date:   Thu, 27 Feb 2020 17:40:31 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Richard Weinberger <richard@....at>,
        Sekhar Nori <nsekhar@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Pratyush Yadav <p.yadav@...com>
Subject: Re: [PATCH v2 01/11] dt-bindings: spi: allow expressing DTR capability

Hi Mark,

On Thu, Feb 27, 2020 at 5:28 PM Mark Brown <broonie@...nel.org> wrote:
> On Thu, Feb 27, 2020 at 05:11:47PM +0100, Boris Brezillon wrote:
> > Pratyush Yadav <p.yadav@...com> wrote:
>
> > > Allow spi devices to express DTR receive and transmit capabilities via
> > > the properties "spi-rx-dtr" and "spi-tx-dtr".
>
> > Is the RX/TX granularity really useful?
>
> It's what we do for other properties, and if this is anything like the
> other things adding extra wiring you can't assume that the ability to
> use the feature for TX implies RX.

Double Transfer Rate uses the same wire.
But as you sample at both the rising and the falling edges of the clock, this
makes the cpha setting meaningless for such transfers, I think ;-)

However, as the future may bring us QDR, perhaps this should not be a
boolean flag, but an integer value?
Cfr. spi-tx-bus-width vs. the original spi-tx-dual/spi-tx-quad proposal.

What would be a good name (as we only need one)? spi-data-phases?

Gr{oetje,eeting}s,

                        Geert

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