Support two new half-duplex SPI implementation restrictions, for links
that talk to TX-only or RX-only devices. (Existing half-duplex flavors
support both transfer directions, just not at the same time.)
Move spi_async() into the spi.c core, and stop inlining it. Then make
that function perform error checks and reject messages that demand more
than the underlying controller can support.
Based on a patch from Marek Szyprowski which did this only for the
bitbanged GPIO driver.
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
568d0697f4