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

From: Marcel Ziswiler
Date: Tue Jun 03 2014 - 02:03:38 EST

On 06/03/2014 12:16 AM, Mark Brown wrote:
On Mon, Jun 02, 2014 at 06:28:37PM +0200, Marcel Ziswiler wrote:
On 06/02/2014 06:11 PM, Stephen Warren wrote:

+CONFIG_SPI_SPIDEV=y

Is this useful with DT? I thought that unlike I2C_CHARDEV, spidev needed
dummy devices to exist in DT for spidev to work? If so, there's not much
point adding the option to defconfig, since people can add it when they
put the dummy devices into DT.

Yes, the Apalis T30 DT I sent actually contains two of them which we call
generic Apalis SPI1 and SPI2 out-of-the-box configured for exactly that.
Without the config enabled though it probably does not make much sense to
include it in the DT so I would consider removing it again.

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.
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