Re: [PATCH/RFC] simple SPI controller on PXA2xx SSP port, refresh

[Stephen Street <stephen@streetfiresound.com>]

On Thu, 2005-10-27 at 19:33 +0800, Mike Lee wrote:
> Dear Stepen
>    I am now writing another controller driver by david's framework.
> But leak of debuging layer, could your loopback driver serve for this
> purpose and how could i use it?
> 

The file pxa2xx_loopback.c should be controller independent, but it does
require that the hardware (in my case the PXA255 NSSP) support a
loopback mode (i.e. tx connected to rx).

To create a loopback device for driver you should include:

static struct pxa2xx_spi_chip loopback_chip_info = {
	.mode = SPI_MODE_3,
	.tx_threshold = 12,
	.rx_threshold = 4,
	.dma_burst_size = 8,
	.bits_per_word = 8,
	.timeout_microsecs = 64,
	.enable_loopback = 1,
};

static struct spi_board_info streetracer_spi_board_info[] __initdata = {
	{
		.modalias = "loopback",
		.max_speed_hz = 3686400,
		.bus_num = 2,
		.chip_select = 3,
		.controller_data = &loopback_chip_info,
	},
};

in your board init code and install the module per your configuration.
Anything written to /dev/slp23 will be echoed back to /dev/slp23 via the
"SPI controller".

Hope this helps!

-Stephen