linux-kernel - Re: [PATCH] spi: Add spi-bits-per-word binding.

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Message-ID: <20170317212143.bogj6efzyvvf24yd@sirena.org.uk>
Date:   Fri, 17 Mar 2017 21:21:43 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Adrian Fiergolski <Adrian.Fiergolski@...n.ch>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>
Subject: Re: [PATCH] spi: Add spi-bits-per-word binding.

On Mon, Mar 13, 2017 at 09:26:04PM +0100, Adrian Fiergolski wrote:
> On 13.03.2017 at 20:57, Geert Uytterhoeven wrote:
> > On Mon, Mar 13, 2017 at 7:12 PM, Adrian Fiergolski
d
> >>> I can't see any way in which it follows from the above that it's a good
> >>> idea to try to override bits per word settings in the device tree, that
> >>> just wastes user time and is an abstraction failure.  We need better
> >>> handling of defaults done purely in the kernel.

> >> If enforcing by device tree specific for a given device driver SPI_CPHA,
> >> SPIC_CPOL, SPI_CS_HIGH, max_speed_hz, etc. if fine form the abstraction
> >> point of view, why it doesn't apply to bits_per_word ?

> > Because unlike polarity, phase, and speed, bits_per_word is a property
> > of the communication protocol.

> > E.g. you can talk to the same EEPROM using different polarities, phase, or
> > speed, but bits_per_word is fixed.

> In this case, currently, what is the proper way to handle SPI
> controllers (spi-xilinx) without 8-bit transmission support ?

As I said above we should fix the handling of defaults such that it is
possible to instantiate a 16 bit using device on a 16 bit supporting
controller; there should be no need to have anything about device tree
in this.

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