linux-kernel - Re: [PATCH 1/2] dt-bindings: spi: dw: add cs-override property

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Message-ID: <20181011134636.GC25351@sirena.org.uk>
Date:   Thu, 11 Oct 2018 14:46:36 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Trent Piepho <tpiepho@...inj.com>
Cc:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "talel@...zon.com" <talel@...zon.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "barakw@...zon.com" <barakw@...zon.com>,
        "ronenk@...zon.com" <ronenk@...zon.com>,
        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>
Subject: Re: [PATCH 1/2] dt-bindings: spi: dw: add cs-override property

On Wed, Oct 10, 2018 at 10:21:51PM +0000, Trent Piepho wrote:

> So that's the problem!  I, like everyone else I suspect, switched to
> using GPIO chip selects with this driver because of this.  I narrowed

That's generally a good idea.

> it down to a CS de-assert when the bus switched from TX to RX, which of
> course makes a SPI register read fail on most devices.  The TX FIFO
> would empty at this point, so that would explain it.

> Did the designers of this IP ever read a SPI device datasheet???

> Got to agree with Mark Brown, why would anyone ever want to NOT have it
> work properly?  The previous behavior is not "alternate correct", it's
> Broken.

This isn't even that unusual an innovation for hardware to have, for
some reason automatic chip select management is *really* popular and
rarely helpful.  It's far from the most entertaining thing I've seen
hardware do.

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