The patch titled
spi: documentation tweaks
has been added to the -mm tree. Its filename is
spi-documentation-tweaks.patch
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------------------------------------------------------
Subject: spi: documentation tweaks
From: David Brownell <david-b@xxxxxxxxxxx>
Update SPI documentation to clarify some areas of recent confusion: clock
polarity takes effect when chipselect goes active; and zero length buffers are
OK in certain cases.
Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/spi/spi-summary | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff -puN Documentation/spi/spi-summary~spi-documentation-tweaks Documentation/spi/spi-summary
--- a/Documentation/spi/spi-summary~spi-documentation-tweaks
+++ a/Documentation/spi/spi-summary
@@ -116,6 +116,13 @@ low order bit. So when a chip's timing
starting low (CPOL=0) and data stabilized for sampling during the
trailing clock edge (CPHA=1), that's SPI mode 1.
+Note that the clock mode is relevant as soon as the chipselect goes
+active. So the master must set the clock to inactive before selecting
+a slave, and the slave can tell the chosen polarity by sampling the
+clock level when its select line goes active. That's why many devices
+support for example both modes 0 and 3: they don't care about polarity,
+and alway clock data in/out on rising clock edges.
+
How do these driver programming interfaces work?
------------------------------------------------
@@ -379,8 +386,14 @@ any more such messages.
+ when bidirectional reads and writes start ... by how its
sequence of spi_transfer requests is arranged;
+ + which I/O buffers are used ... each spi_transfer wraps a
+ buffer for each transfer direction, supporting full duplex
+ (two pointers, maybe the same one in both cases) and half
+ duplex (one pointer is NULL) transfers;
+
+ optionally defining short delays after transfers ... using
- the spi_transfer.delay_usecs setting;
+ the spi_transfer.delay_usecs setting (this delay can be the
+ only protocol effect, if the buffer length is zero);
+ whether the chipselect becomes inactive after a transfer and
any delay ... by using the spi_transfer.cs_change flag;
_
Patches currently in -mm which might be from david-b@xxxxxxxxxxx are
origin.patch
git-acpi.patch
git-arm.patch
git-avr32.patch
git-input.patch
input-add-debouncing-for-generic-gpio-input-device-gpio_keyc.patch
jffs2-summary-allocation-dont-use-vmalloc.patch
fix-gregkh-usb-usb-ohci-port-reset-paranoia-timeout.patch
spi-pxa2xx_spi-sparse-fixes.patch
atmel_spi-support-zero-length-transfer.patch
rtc-avoid-legacy-drivers-with-generic-framework.patch
rtc-avoid-legacy-drivers-with-generic-framework-update.patch
rtc-isl1208-new-style-conversion-and-minor-bug-fixes.patch
rtc-isl1208-new-style-conversion-and-minor-bug-fixes-checkpatch-fixes.patch
rtc-pcf8563-new-style-conversion.patch
rtc-pcf8563-new-style-conversion-checkpatch-fixes.patch
rtc-pcf8563-new-style-conversion-checkpatch-fixes-fix.patch
rtc-x1205-new-style-conversion.patch
rtc-x1205-new-style-conversion-checkpatch-fixes.patch
rtc-silence-section-mismatch-warning-in-rtc-test.patch
make-ds1511_rtc_readset_time-static.patch
kerneldoc-for-linux-clkh.patch
kerneldoc-for-linux-clkh-fix.patch
rtc-rtc-rs5c372-fix-up-null-name-in-transfer-error-path.patch
rtc-rtc-rs5c372-smbus-conversion-support.patch
rtc-rtc-rs5c732-add-support-for-ricoh-r2025s-d-rtc.patch
rtc-replace-remaining-__function__-occurrences.patch
gpiochip_reserve-fix-2.patch
remove-duplicated-unlikely-in-is_err.patch
spi-documentation-tweaks.patch
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