From: "Woodhouse, David" <dwmw@amazon.co.uk>
To: "Shenhar, Talel" <talel@amazon.com>,
"broonie@kernel.org" <broonie@kernel.org>
Cc: "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Krupnik, Ronen" <ronenk@amazon.com>,
"Wasserstrom, Barak" <barakw@amazon.com>,
"robh+dt@kernel.org" <robh+dt@kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: spi: dw: add cs-override property
Date: Wed, 10 Oct 2018 11:58:40 +0000 [thread overview]
Message-ID: <ba83a08073614d9244c01218da28fe3e23f3bbc2.camel@amazon.co.uk> (raw)
In-Reply-To: <20181010112753.GC6294@sirena.org.uk>
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On Wed, 2018-10-10 at 12:27 +0100, Mark Brown wrote:
> On Wed, Oct 10, 2018 at 02:23:40PM +0300, Talel Shenhar wrote:
> > On 10/10/2018 01:18 PM, Mark Brown wrote:
> > > On Wed, Oct 10, 2018 at 10:08:12AM +0300, Talel Shenhar wrote:
> > > > The dw spi controller has an auto-deselect of Chip-Select, in case there is
> > > > no data inside the Tx FIFO. While working on platforms with Alpine chips,
> > > Why would we ever want to use this behaviour? It will be broken for any
> > > non-trivial SPI message such as those made with multiple transfers
> > > anyway. Why not just unconditionally control it manually?
> > This behavior (auto-deselect of Chip-Select) is the default behavior of dw spi controller hw.
> > On Alpine chip there is additional behavior added to the dw spi controller hw that allows the sw to disable this behavior.
> > This patch allows the dw driver to enable this hw workaround and add the needed sw manual control for it.
>
> If this is a modified IP with additional features then it should be
> given a new compatible string rather than having a property - it's not
> just configuration of the existing IP, it's a new thing and we may find
> there are other quirks that have to be taken care of for it.
No.
It's an extension of the existing IP which is explicitly designed to be
compatible with existing drivers via an opt-in feature.
Which is exactly what we've spent the last decade or two trying to beat
hardware designers into doing, instead of randomly breaking
compatibility for no good reason.
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Amazon Development Centre (London) Ltd. Registered in England and Wales with registration number 04543232 with its registered office at 1 Principal Place, Worship Street, London EC2A 2FA, United Kingdom.
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next prev parent reply other threads:[~2018-10-10 11:58 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-10 7:08 [PATCH 1/2] dt-bindings: spi: dw: add cs-override property Talel Shenhar
2018-10-10 7:08 ` [PATCH 2/2] dw: spi: add 'cs-override' DT property support Talel Shenhar
2018-10-10 10:18 ` [PATCH 1/2] dt-bindings: spi: dw: add cs-override property Mark Brown
2018-10-10 10:34 ` Talel Shenhar
2018-10-10 11:29 ` David Woodhouse
2018-10-10 11:23 ` Talel Shenhar
2018-10-10 11:27 ` Mark Brown
2018-10-10 11:58 ` Woodhouse, David [this message]
2018-10-10 12:27 ` Mark Brown
2018-10-10 22:52 ` Trent Piepho
2018-10-10 15:15 ` [PATCH 1/2] dt-bindings: spi: dw: add compatible for Alpine spi controller Talel Shenhar
2018-10-10 15:15 ` [PATCH 2/2] dw: spi: add support " Talel Shenhar
2018-10-10 22:08 ` Trent Piepho
2018-10-11 11:20 ` [PATCH 1/2] dt-bindings: spi: dw: add compatible for Amazon's " Talel Shenhar
2018-10-11 11:20 ` [PATCH 2/2] dw: spi: add support " Talel Shenhar
2018-10-11 14:58 ` Applied "dw: spi: add support for Amazon's Alpine spi controller" to the spi tree Mark Brown
2018-10-11 13:44 ` [PATCH 1/2] dt-bindings: spi: dw: add compatible for Amazon's Alpine spi controller Mark Brown
2018-10-11 14:58 ` Applied "spi: dw: add compatible for Amazon's Alpine spi controller" to the spi tree Mark Brown
2018-10-11 11:22 ` [PATCH 2/2] dw: spi: add support for Alpine spi controller Talel Shenhar
2018-10-10 22:21 ` [PATCH 1/2] dt-bindings: spi: dw: add cs-override property Trent Piepho
2018-10-11 7:39 ` Talel Shenhar
2018-10-11 13:46 ` Mark Brown
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