xhci: dbc: Allow users to modify DbC poll interval via sysfs

[ Upstream commit de3edd47 ]

xhci DbC driver polls the host controller for DbC events at a reduced
rate when DbC is enabled but there are no active data transfers.

Allow users to modify this reduced poll interval via dbc_poll_interval_ms
sysfs entry. Unit is milliseconds and accepted range is 0 to 5000.
Max interval of 5000 ms is selected as it matches the common 5 second
timeout used in usb stack.
Default value is 64 milliseconds.

A long interval is useful when users know there won't be any activity
on systems connected via DbC for long periods, and want to avoid
battery drainage due to unnecessary CPU usage.

Example being Android Debugger (ADB) usage over DbC on ChromeOS systems
running Android Runtime.

[minor changes and rewording -Mathias]

Co-developed-by: Samuel Jacob <samjaco@google.com>
Signed-off-by: Samuel Jacob <samjaco@google.com>
Signed-off-by: Uday M Bhat <uday.m.bhat@intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240626124835.1023046-5-mathias.nyman@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: f3d12ec8 ("xhci: dbc: fix bogus 1024 byte prefix if ttyDBC read races with stall event")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>