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

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Message-ID: <20200227164425.GF4062@sirena.org.uk>
Date:   Thu, 27 Feb 2020 16:44:25 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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

On Thu, Feb 27, 2020 at 05:40:31PM +0100, Geert Uytterhoeven wrote:
> On Thu, Feb 27, 2020 at 5:28 PM Mark Brown <broonie@...nel.org> wrote:

> > 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 is it still on either the TX or RX signals?

> 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 ;-)

Might affect what the first bit is possibly?

> 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?

Sounds reasonable, apart from the increasingly vague connection with
something that's recognizably SPI :P

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