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-rw-r--r--Documentation/spi/spi-summary58
1 files changed, 46 insertions, 12 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index 4884cb3..7312ec1 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -1,7 +1,7 @@
Overview of Linux kernel SPI support
====================================
-21-May-2007
+02-Feb-2012
What is SPI?
------------
@@ -483,9 +483,9 @@ also initialize its own internal state. (See below about bus numbering
and those methods.)
After you initialize the spi_master, then use spi_register_master() to
-publish it to the rest of the system. At that time, device nodes for
-the controller and any predeclared spi devices will be made available,
-and the driver model core will take care of binding them to drivers.
+publish it to the rest of the system. At that time, device nodes for the
+controller and any predeclared spi devices will be made available, and
+the driver model core will take care of binding them to drivers.
If you need to remove your SPI controller driver, spi_unregister_master()
will reverse the effect of spi_register_master().
@@ -521,21 +521,53 @@ SPI MASTER METHODS
** 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
- will normally happen later, after other transfers complete, and
- if the controller is idle it will need to be kickstarted.
-
master->cleanup(struct spi_device *spi)
Your controller driver may use spi_device.controller_state to hold
state it dynamically associates with that device. If you do that,
be sure to provide the cleanup() method to free that state.
+ master->prepare_transfer_hardware(struct spi_master *master)
+ This will be called by the queue mechanism to signal to the driver
+ that a message is coming in soon, so the subsystem requests the
+ driver to prepare the transfer hardware by issuing this call.
+ This may sleep.
+
+ master->unprepare_transfer_hardware(struct spi_master *master)
+ This will be called by the queue mechanism to signal to the driver
+ that there are no more messages pending in the queue and it may
+ relax the hardware (e.g. by power management calls). This may sleep.
+
+ master->transfer_one_message(struct spi_master *master,
+ struct spi_message *mesg)
+ The subsystem calls the driver to transfer a single message while
+ queuing transfers that arrive in the meantime. When the driver is
+ finished with this message, it must call
+ spi_finalize_current_message() so the subsystem can issue the next
+ transfer. This may sleep.
+
+ DEPRECATED METHODS
+
+ 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
+ will normally happen later, after other transfers complete, and
+ if the controller is idle it will need to be kickstarted. This
+ method is not used on queued controllers and must be NULL if
+ transfer_one_message() and (un)prepare_transfer_hardware() are
+ implemented.
+
SPI MESSAGE QUEUE
-The bulk of the driver will be managing the I/O queue fed by transfer().
+If you are happy with the standard queueing mechanism provided by the
+SPI subsystem, just implement the queued methods specified above. Using
+the message queue has the upside of centralizing a lot of code and
+providing pure process-context execution of methods. The message queue
+can also be elevated to realtime priority on high-priority SPI traffic.
+
+Unless the queueing mechanism in the SPI subsystem is selected, the bulk
+of the driver will be managing the I/O queue fed by the now deprecated
+function transfer().
That queue could be purely conceptual. For example, a driver used only
for low-frequency sensor access might be fine using synchronous PIO.
@@ -561,4 +593,6 @@ Stephen Street
Mark Underwood
Andrew Victor
Vitaly Wool
-
+Grant Likely
+Mark Brown
+Linus Walleij