The patch titled
spi: documentation: emphasise spi_master.setup() semantics
has been added to the -mm tree. Its filename is
spi-documentation-emphasise-spi_mastersetup-semantics.patch
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Subject: spi: documentation: emphasise spi_master.setup() semantics
From: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/spi/spi-summary | 6 ++++++
include/linux/spi/spi.h | 7 ++++++-
2 files changed, 12 insertions(+), 1 deletion(-)
diff -puN Documentation/spi/spi-summary~spi-documentation-emphasise-spi_mastersetup-semantics Documentation/spi/spi-summary
--- a/Documentation/spi/spi-summary~spi-documentation-emphasise-spi_mastersetup-semantics
+++ a/Documentation/spi/spi-summary
@@ -511,10 +511,16 @@ SPI MASTER METHODS
This sets up the device clock rate, SPI mode, and word sizes.
Drivers may change the defaults provided by board_info, and then
call spi_setup(spi) to invoke this routine. It may sleep.
+
Unless each SPI slave has its own configuration registers, don't
change them right away ... otherwise drivers could corrupt I/O
that's in progress for other SPI devices.
+ ** BUG ALERT: for some reason the first version of
+ ** many spi_master drivers seems to get this wrong.
+ ** When you code setup(), ASSUME that the controller
+ ** is actively processing transfers for another device.
+
master->transfer(struct spi_device *spi, struct spi_message *message)
This must not sleep. Its responsibility is arrange that the
transfer happens and its complete() callback is issued. The two
diff -puN include/linux/spi/spi.h~spi-documentation-emphasise-spi_mastersetup-semantics include/linux/spi/spi.h
--- a/include/linux/spi/spi.h~spi-documentation-emphasise-spi_mastersetup-semantics
+++ a/include/linux/spi/spi.h
@@ -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
_
Patches currently in -mm which might be from dbrownell@xxxxxxxxxxxxxxxxxxxxx are
linux-next.patch
spi-documentation-emphasise-spi_mastersetup-semantics.patch
rtc-rtc-ds1307-add-ds3231.patch
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