aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/spi/spi-summary
diff options
context:
space:
mode:
authorDavid Brownell <dbrownell@users.sourceforge.net>2009-04-21 15:24:49 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-21 16:41:50 -0400
commit6e538aaf50ae782a890cbc02c27950448d8193e1 (patch)
tree0e61cacadc2fe403f411e52ba18539bdd52b17e2 /Documentation/spi/spi-summary
parent14fadca793e39742f442df53391cdd1437b9262f (diff)
spi: documentation: emphasise spi_master.setup() semantics
This is a doc-only patch which I hope will reduce the number of spi_master controller driver patches starting out with a common implementation bug. (As in: almost every spi_master driver I see starts out with its version of this bug. Sigh.) It just re-emphasizes that the setup() method may be called for one device while a transfer is active on another ... which means that most driver implementations shouldn't touch any registers. 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>
Diffstat (limited to 'Documentation/spi/spi-summary')
-rw-r--r--Documentation/spi/spi-summary6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index 0f5122eb282b..4a02d2508bc8 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -511,10 +511,16 @@ SPI MASTER METHODS
511 This sets up the device clock rate, SPI mode, and word sizes. 511 This sets up the device clock rate, SPI mode, and word sizes.
512 Drivers may change the defaults provided by board_info, and then 512 Drivers may change the defaults provided by board_info, and then
513 call spi_setup(spi) to invoke this routine. It may sleep. 513 call spi_setup(spi) to invoke this routine. It may sleep.
514
514 Unless each SPI slave has its own configuration registers, don't 515 Unless each SPI slave has its own configuration registers, don't
515 change them right away ... otherwise drivers could corrupt I/O 516 change them right away ... otherwise drivers could corrupt I/O
516 that's in progress for other SPI devices. 517 that's in progress for other SPI devices.
517 518
519 ** BUG ALERT: for some reason the first version of
520 ** many spi_master drivers seems to get this wrong.
521 ** When you code setup(), ASSUME that the controller
522 ** is actively processing transfers for another device.
523
518 master->transfer(struct spi_device *spi, struct spi_message *message) 524 master->transfer(struct spi_device *spi, struct spi_message *message)
519 This must not sleep. Its responsibility is arrange that the 525 This must not sleep. Its responsibility is arrange that the
520 transfer happens and its complete() callback is issued. The two 526 transfer happens and its complete() callback is issued. The two