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    gpio: mcp23s08 handles multiple chips per chipselect · 8f1cc3b1
    David Brownell 提交于
    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: NDavid Brownell <dbrownell@users.sourceforge.net>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    8f1cc3b1
mcp23s08.c 9.5 KB