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authorDavid Brownell <david-b@pacbell.net>2006-04-03 18:49:04 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2006-05-16 17:33:57 -0400
commita020ed7521a9737bcf3e34eb880867c60c3c68d0 (patch)
tree52941e00b05df6c1bfe228fd193fdb09cf963d15 /Documentation/spi
parentccf77cc4af5b048e20cfd9327fcc286cb69c34cc (diff)
[PATCH] SPI: busnum == 0 needs to work
We need to be able to have a "SPI bus 0" matching chip numbering; but that number was wrongly used to flag dynamic allocation of a bus number. This patch resolves that issue; now negative numbers trigger dynamic alloc. It also updates the how-to-write-a-controller-driver overview to mention this stuff. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/spi')
-rw-r--r--Documentation/spi/spi-summary34
1 files changed, 33 insertions, 1 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index a5ffba33a35..068732d3227 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -414,7 +414,33 @@ to get the driver-private data allocated for that device.
414The driver will initialize the fields of that spi_master, including the 414The driver will initialize the fields of that spi_master, including the
415bus number (maybe the same as the platform device ID) and three methods 415bus number (maybe the same as the platform device ID) and three methods
416used to interact with the SPI core and SPI protocol drivers. It will 416used to interact with the SPI core and SPI protocol drivers. It will
417also initialize its own internal state. 417also initialize its own internal state. (See below about bus numbering
418and those methods.)
419
420After you initialize the spi_master, then use spi_register_master() to
421publish it to the rest of the system. At that time, device nodes for
422the controller and any predeclared spi devices will be made available,
423and the driver model core will take care of binding them to drivers.
424
425If you need to remove your SPI controller driver, spi_unregister_master()
426will reverse the effect of spi_register_master().
427
428
429BUS NUMBERING
430
431Bus numbering is important, since that's how Linux identifies a given
432SPI bus (shared SCK, MOSI, MISO). Valid bus numbers start at zero. On
433SOC systems, the bus numbers should match the numbers defined by the chip
434manufacturer. For example, hardware controller SPI2 would be bus number 2,
435and spi_board_info for devices connected to it would use that number.
436
437If you don't have such hardware-assigned bus number, and for some reason
438you can't just assign them, then provide a negative bus number. That will
439then be replaced by a dynamically assigned number. You'd then need to treat
440this as a non-static configuration (see above).
441
442
443SPI MASTER METHODS
418 444
419 master->setup(struct spi_device *spi) 445 master->setup(struct spi_device *spi)
420 This sets up the device clock rate, SPI mode, and word sizes. 446 This sets up the device clock rate, SPI mode, and word sizes.
@@ -431,6 +457,9 @@ also initialize its own internal state.
431 state it dynamically associates with that device. If you do that, 457 state it dynamically associates with that device. If you do that,
432 be sure to provide the cleanup() method to free that state. 458 be sure to provide the cleanup() method to free that state.
433 459
460
461SPI MESSAGE QUEUE
462
434The bulk of the driver will be managing the I/O queue fed by transfer(). 463The bulk of the driver will be managing the I/O queue fed by transfer().
435 464
436That queue could be purely conceptual. For example, a driver used only 465That queue could be purely conceptual. For example, a driver used only
@@ -440,6 +469,9 @@ But the queue will probably be very real, using message->queue, PIO,
440often DMA (especially if the root filesystem is in SPI flash), and 469often DMA (especially if the root filesystem is in SPI flash), and
441execution contexts like IRQ handlers, tasklets, or workqueues (such 470execution contexts like IRQ handlers, tasklets, or workqueues (such
442as keventd). Your driver can be as fancy, or as simple, as you need. 471as keventd). Your driver can be as fancy, or as simple, as you need.
472Such a transfer() method would normally just add the message to a
473queue, and then start some asynchronous transfer engine (unless it's
474already running).
443 475
444 476
445THANKS TO 477THANKS TO