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authorDavid Brownell <david-b@pacbell.net>2006-01-08 13:34:25 -0800
committerGreg Kroah-Hartman <gregkh@suse.de>2006-01-13 16:29:55 -0800
commit0c868461fcb8413cb9f691d68e5b99b0fd3c0737 (patch)
treeb43db6239f5d72a279b35b14de85cf34d8f6bc74 /Documentation/spi/spi-summary
parentb885244eb2628e0b8206e7edaaa6a314da78e9a4 (diff)
downloadblackbird-op-linux-0c868461fcb8413cb9f691d68e5b99b0fd3c0737.tar.gz
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[PATCH] SPI core tweaks, bugfix
This includes various updates to the SPI core: - Fixes a driver model refcount bug in spi_unregister_master() paths. - The spi_master structures now have wrappers which help keep drivers from needing class-level get/put for device data or for refcounts. - Check for a few setup errors that would cause oopsing later. - Docs say more about memory management. Highlights the use of DMA-safe i/o buffers, and zero-initializing spi_message and such metadata. - Provide a simple alloc/free for spi_message and its spi_transfer; this is only one of the possible memory management policies. Nothing to break code that already works. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/spi/spi-summary')
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diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index c6152d1ff2b0..761debf748e9 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -363,6 +363,22 @@ upper boundaries might include sysfs (especially for sensor readings),
the input layer, ALSA, networking, MTD, the character device framework,
or other Linux subsystems.
+Note that there are two types of memory your driver must manage as part
+of interacting with SPI devices.
+
+ - I/O buffers use the usual Linux rules, and must be DMA-safe.
+ You'd normally allocate them from the heap or free page pool.
+ Don't use the stack, or anything that's declared "static".
+
+ - The spi_message and spi_transfer metadata used to glue those
+ I/O buffers into a group of protocol transactions. These can
+ be allocated anywhere it's convenient, including as part of
+ other allocate-once driver data structures. Zero-init these.
+
+If you like, spi_message_alloc() and spi_message_free() convenience
+routines are available to allocate and zero-initialize an spi_message
+with several transfers.
+
How do I write an "SPI Master Controller Driver"?
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