i2c: mux: pca954x: allow management of device idle state via sysfs
The behaviour, by default, to not deselect after each transfer is
unsafe when there is a device with an address that conflicts with
another device on another mux on the same parent bus, and it
may not be convenient to use devicetree to set the deselect mux,
e.g. when running on x86_64 when ACPI is used to discover most of the
device hierarchy.
Therefore, provide the ability to set the idle state behaviour using a
new sysfs file, idle_state as a complement to the method of
instantiating the device via sysfs. The possible behaviours are
disconnect, i.e. to deselect all channels from the mux, as-is (the
default), i.e. leave the last channel selected, and set a
predetermined channel.
The current behaviour of leaving the channel as-is after each
transaction is preserved.
Signed-off-by: Robert Shearman <robert.shearman@att.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
2019-02-28 19:43:43 +08:00
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What: /sys/bus/i2c/.../idle_state
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Date: January 2019
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KernelVersion: 5.2
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Contact: Robert Shearman <robert.shearman@att.com>
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Description:
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Value that exists only for mux devices that can be
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written to control the behaviour of the multiplexer on
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idle. Possible values:
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2020-10-30 15:40:39 +08:00
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=========== ===============================================
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-2 disconnect on idle, i.e. deselect the last used
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channel, which is useful when there is a device
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with an address that conflicts with another
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device on another mux on the same parent bus.
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-1 leave the mux as-is, which is the most optimal
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setting in terms of I2C operations and is the
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default mode.
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0..<nchans> set the mux to a predetermined channel,
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which is useful if there is one channel that is
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used almost always, and you want to reduce the
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latency for normal operations after rare
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transactions on other channels
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=========== ===============================================
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