Re: Generic MMC-over-SPI binding?

On Tuesday 08 January 2008, Simon Richter wrote:

in an embedded system similar to the lite5200 board, there is an MMC 
card socket connected to one of the PSCs. Ideally, I'd like to express 
this fact via the device tree and have the kernel bind the mmc-spi 
driver to the SPI interface, but I cannot find any place where to insert 
this code that I feel comfortable with.
...
Any ideas?

One way you could do it would be to have an spi_board_info in the
way that mpc832x_spi_init does it, but that would not make use of the
device tree.

What would probably be a better way is to call spi_new_device()
from the mpc52xx_psc_spi driver, with an spi_board_info you generate
on the fly for each child of the spi controller.

The important part where this connects to the mmc-spi driver is that
you need to set spi_board_info->modalias to "mmc-spi", if the
device node can be identified as an mmc card.
We'd have to define a list of valid identifications of SPI devices
in the device tree, and teach the SPI drivers how they relate to
linux device drivers like mmc-spi.

Since that part of the code would be used by all device tree based
SPI master drivers, it should be in a separate module, which can
consist of a single exported function, like (paraphrased):

void spi_of_scan_master(struct spi_master *master)
{
	struct device_node *child;
	of_dev_for_each_child(master->dev->node, child) {
		struct spi_board_info *info;
		info = kzalloc(sizeof (*info), GFP_KERNEL);
		if (of_device_is_compatible(child, "spi,mmc"))
			strcpy(info->modalias, "mmc-spi");
		else if (of_device_is_compatible(child, "spi,foo"))
			strcpy(info->modalias, "foo");
		else
			strcpy(info->modalias, "");

		info->irq = irq_of_parse_and_map(child);
		
		spi_new_device(master, child);
	}
}

Then you call that function after registering the master, from
mpc52xx_psc_spi_of_probe.

	Arnd <><