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>
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 2cc43fa..a0faa18 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -245,7 +245,12 @@
*/
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