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This can be used to check if a device supports sync_state() callbacks and therefore keeps resources left on by the bootloader enabled till all its consumers have probed. This can also be used to check if sync_state() has been called for a device or whether it is still trying to keep resources enabled because they were left enabled by the bootloader and all its consumers haven't probed yet. Signed-off-by: Saravana Kannan <saravanak@google.com> Link: https://lore.kernel.org/r/20200521191800.136035-3-saravanak@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
24 lines
1.1 KiB
Text
24 lines
1.1 KiB
Text
What: /sys/devices/.../state_synced
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Date: May 2020
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Contact: Saravana Kannan <saravanak@google.com>
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Description:
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The /sys/devices/.../state_synced attribute is only present for
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devices whose bus types or driver provides the .sync_state()
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callback. The number read from it (0 or 1) reflects the value
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of the device's 'state_synced' field. A value of 0 means the
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.sync_state() callback hasn't been called yet. A value of 1
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means the .sync_state() callback has been called.
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Generally, if a device has sync_state() support and has some of
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the resources it provides enabled at the time the kernel starts
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(Eg: enabled by hardware reset or bootloader or anything that
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run before the kernel starts), then it'll keep those resources
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enabled and in a state that's compatible with the state they
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were in at the start of the kernel. The device will stop doing
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this only when the sync_state() callback has been called --
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which happens only when all its consumer devices are registered
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and have probed successfully. Resources that were left disabled
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at the time the kernel starts are not affected or limited in
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any way by sync_state() callbacks.
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