Re: [PATCH 1/3] mmc: add support for power-on sequencing through DT

[Arnd Bergmann <arnd@arndb.de>]

On Saturday 15 February 2014 12:27:33 Russell King - ARM Linux wrote:
> On Sat, Feb 15, 2014 at 01:18:02PM +0100, Arnd Bergmann wrote:
> > If a wlan adapter has both SPI and SDIO front-ends, the external
> > dependencies (reset, clock, voltage, ...) will be the same, and
> > from the kernel perspective the main difference is that SPI cannot
> > be probed at all, while SDIO can be probed as long as the device
> > is powered on already.
> 
> Remember that MMC/SD/SDIO cards can be driven by either a MMC host
> interface, or a SPI interface.  Both are probe-able.

I knew about MMC/SD cards being required to understand simple SPI,
I wasn't sure about SDIO. My understanding however is that you
have to use the mmc_spi host driver to actually use MMC/SD devices
as a block device, and that requires having either a DT description
for the host or an spi_board_info, which I would not consider
discoverable.

For spi-mode SDIO devices I'm assuming it's similar, except that
you'd describe the actual SDIO device in the board info rather than
create a fake SDIO controller. Still not discoverable unless I'm
missing your point.

	Arnd