The merge window for 2.6.24 should open up any day now, so it's
probably time for me to detail what I intend to cram in there.
This release will probably be one of the biggest ones for the MMC layer
so far. The major pieces are SDIO and SPI support, but there are
several small nuggets as well.
SDIO
----
Gone are the days of having to rely on proprietary stacks for SDIO
support in Linux. So no more spotty support for hosts and possible GPL
problems. SDIO will now be a standard feature of Linux.
The model is largely based on PCI. All the memory operations they have
(readX/writeX and friends) exist in an equivalent manner for SDIO. We
also have the readsb() and writesb() functions which exist only on some
platforms for "normal" I/O. (For those not familiar with these
functions, they write every byte of a block of data into a single
byte in the address space.)
The big difference from other buses is that you have to hold the host
lock (which has gotten SDIO wrappers for ease of use), and that all I/O
operations may sleep.
There has been some talk about asynchronous requests, but that doesn't
really make much sense for a bus like SDIO where you don't interleave
transfers.
Interrupt support is also there and uses an interface similar to other
buses. It is called from process context though (currently a dedicated
kernel thread handles interrupts). Your ISR will also be called with
the host lock held, so keep the ISR short and try delegate what you
can. The only MUST is that you must remove the interrupt source before
you exit.
There are currently three working drivers for this new stack:
- sdio_uart: A driver for the standardised GPS and UART interfaces.
Currently we only know how the GPS system works, so UART is only a
future possibility.
- libertas_sdio: Support for Marvell's 8686 Libertas wifi chip. Will
be merged late in the merge window as there are some interdependencies
between my tree and the libertas tree.
- hci_sdio: A driver for the standardised bluet...
