linux-kernel - Re: [PATCH 1/2] spi: support inter-word delay requirement for devices

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Message-ID: <20190125174713.GA6939@sirena.org.uk>
Date:   Fri, 25 Jan 2019 17:47:13 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Jonas Bonn <jonas@...rbonn.se>
Cc:     Baolin Wang <baolin.wang@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/2] spi: support inter-word delay requirement for devices

On Fri, Jan 25, 2019 at 01:06:45PM +0100, Jonas Bonn wrote:
> On 25/01/2019 12:53, Baolin Wang wrote:
> > On Fri, 25 Jan 2019 at 19:44, Jonas Bonn <jonas@...rbonn.se> wrote:

> > Can we configure it at runtime by the device rather than at DT time by
> > the controller? If yes, we already have a patch for this, please
> > check:

> It's a characteristic of the SPI slave, in the same sense as CPOL/CPHA are,
> and therefore it makes sense to specify it in the device tree.

No, that doesn't follow at all.  There's two bits here - where the
configuration gets done and the mechanism by which it gets done.  If
something in DT is completely orthogonal to which device it is a
property of.

> Having this as device property rather than a transfer property allows this
> to be configured one time in setup() rather than having to fiddle with the
> configuration register for every transfer.

That doesn't mean that the coniguration should be done in DT though, and
given that this presumably is a property of the device there seems to be
no reason why we'd have it in DT - if every instance of the device is
going to need to set the property we should just figure it out from the
compatble string instead.

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