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authorDavid Brownell <dbrownell@users.sourceforge.net>2009-06-30 11:41:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-30 18:56:00 -0700
commit70d6027ff2bc8bab180273b77e7ab3e8a62cca51 (patch)
tree1b8e13ffd71c587dcff60933d69a9ff2edb60f0d /drivers/mmc/host/mmc_spi.c
parentb55f627feeb9d48fdbde3835e18afbc76712e49b (diff)
spi: add spi_master flag word
Add a new spi_master.flags word listing constraints relevant to that controller. Define the first constraint bit: a half duplex restriction. Include that constraint in the OMAP1 MicroWire controller driver. Have the mmc_spi host be the first customer of this flag. Its coding relies heavily on full duplex transfers, so it must fail when the underlying controller driver won't perform them. (The spi_write_then_read routine could use it too: use the temporarily-withdrawn full-duplex speedup unless this flag is set, in which case the existing code applies. Similarly, any spi_master implementing only SPI_3WIRE should set the flag.) Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/mmc/host/mmc_spi.c')
-rw-r--r--drivers/mmc/host/mmc_spi.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index 240608cc7ae..a461017ce5c 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1313,6 +1313,12 @@ static int mmc_spi_probe(struct spi_device *spi)
struct mmc_spi_host *host;
int status;
+ /* We rely on full duplex transfers, mostly to reduce
+ * per-transfer overheads (by making fewer transfers).
+ */
+ if (spi->master->flags & SPI_MASTER_HALF_DUPLEX)
+ return -EINVAL;
+
/* MMC and SD specs only seem to care that sampling is on the
* rising edge ... meaning SPI modes 0 or 3. So either SPI mode
* should be legit. We'll use mode 0 since the steady state is 0,