linux-kernel - Re: [PATCH 2/3] arm: tegra: enable igb, stmpe, i2c chardev, spidev, lm95245, pwm leds

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Date:	Tue, 3 Jun 2014 10:45:37 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Marcel Ziswiler <marcel@...wiler.com>
Cc:	Stephen Warren <swarren@...dotorg.org>, thierry.reding@...il.com,
	linux@....linux.org.uk, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, stefan@...er.ch
Subject: Re: [PATCH 2/3] arm: tegra: enable igb, stmpe, i2c chardev, spidev,
 lm95245, pwm leds

On Tue, Jun 03, 2014 at 08:02:37AM +0200, Marcel Ziswiler wrote:
> On 06/03/2014 12:16 AM, Mark Brown wrote:

> >Your DT is broken if it's got a "spidev" node in it, you should be
> >describing the hardware not the Linux implementation of the software.
> >It would be really nice if we had a good way of handling this but we
> >don't yet.

> I strongly disagree, it almost perfectly describes the hardware. Unlike on
> I2c where modelling a bus is enough to allow generic user space access
> unfortunately on SPI this is not enough as it requires a specific
> chip-select as well. This is exactly what spidev does and maps to our
> hardware perfectly which has one dedicated chip-select per SPI bus on a
> dedicated header which allows our customers out-of-the-box spidev user space
> access to almost any SPI device connected to those buses just like with
> i2c-devs on I2C buses.

When you say "generic user space access" you are describing a specific
detail of how this device happens to be controlled with your software.
This is not a description of your hardware, it is a description of how
it is controlled with your current software.

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