[spi-devel-general] [PATCH v3 0/2] spi: driver for Cirrus EP93xx SPI controller

[Mika Westerberg]

On Sat, Apr 17, 2010 at 07:43:23PM +0100, Martin Guy wrote:
> 
> There's a further strangeness when a board has a single SPI device not
> using any GPIO chip select. At present, clients seem to need to
> declare that they have 1 chip select and to provide an empty
> cs_control function that does nothing. For example:
> 
> static void null_cs_control(unsigned cs, unsigned value, void *data) {
>        /* Sim.One only has MMC card and no GPIO chip select logic */
> }
> 
> static struct ep93xx_spi_info simone_spi_info = {
>        .num_chipselect = 1,
>        .cs_control     = null_cs_control,
>        .data           = NULL,
> };
> ...
> static void __init simone_init_machine(void)
> {
> ...
>        spi_register_board_info(simone_spi_board_info,
> ARRAY_SIZE(simone_spi_board_info));
>        ep93xx_register_spi(&simone_spi_info);
> ...
> 
> Allowing cs_control to be NULL would do away with the empty function, but
> when I just tried with num_chipselect = 0 the device did not appear. There
> may be a better solution.

There is a check in spi_master_register() where num_chipselect should be at
least 1. This is probably why it failed in your case.

However, I can add check to the driver that NULL cs_control is ok.

Thanks,
MW