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spi: documentation: emphasise spi_master.setup() semantics

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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>
This commit is contained in:
David Brownell 2009-04-21 12:24:49 -07:00 • committed by Linus Torvalds
parent 14fadca793
commit 6e538aaf50
2 changed files with 12 additions and 1 deletions
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7
include/linux/spi/spi.h
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@ -245,7 +245,12 @@ struct spi_master {
*/
u16 dma_alignment;
/* setup mode and clock, etc (spi driver may call many times) */
/* Setup mode and clock, etc (spi driver may call many times).
*
* IMPORTANT: this may be called when transfers to another
* device are active. DO NOT UPDATE SHARED REGISTERS in ways
* which could break those transfers.
*/
int (*setup)(struct spi_device *spi);
/* bidirectional bulk transfers