path: root/Documentation/bt8xxgpio.txt
diff options
authorDavid Brownell <>2008-07-25 01:46:09 -0700
committerLinus Torvalds <>2008-07-25 10:53:30 -0700
commit8f1cc3b10e6ee0c5c7c8ed27f8771c4f252b4862 (patch)
treea64611af44cf46aea2e2b145fad85042bb647a3d /Documentation/bt8xxgpio.txt
parentd8f388d8dc8d4f36539dd37c1fff62cc404ea0fc (diff)
gpio: mcp23s08 handles multiple chips per chipselect
Teach the mcp23s08 driver about a curious feature of these chips: up to four of them can share the same chipselect, with the SPI signals wired in parallel, by matching two bits in the first protocol byte against two address lines on the chip. This is handled by three software changes: * Platform data now holds an array of per-chip structs, not just one chip's address and pullup configuration. * Probe() and remove() now use another level of structure, wrapping an instance of the original structure for each mcp23s08 chip sharing that chipselect. * The HAEN bit is set, so that the hardware address bits can no longer be ignored (boot firmware may not have enabled them). The "one struct per chip" preserves the guts of the current code, but platform_data will need minor changes. OLD: /* incorrect "slave" ID may not have mattered */ .slave = 3, .pullups = BIT(3) | BIT(1) | BIT(0), NEW: /* slave address _must_ match chip's wiring */ .chip[3] = { .is_present = true, .pullups = BIT(3) | BIT(1) | BIT(0), }, There's no change in how things _behave_ for spi_device nodes with a single mcp23s08 chip. New multi-chip configurations assign GPIOs in sequence, without holes. The spi_device just resembles a bigger controller, but internally it has multiple gpio_chip instances. Signed-off-by: David Brownell <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'Documentation/bt8xxgpio.txt')
0 files changed, 0 insertions, 0 deletions