diff options
Diffstat (limited to 'Documentation/spi/spi-summary')
| -rw-r--r-- | Documentation/spi/spi-summary | 58 |
1 files changed, 46 insertions, 12 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary index 4884cb33845..7312ec14dd8 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 |