ACPI: restore comment justifying 'extra' P_LVLx access
While trying to look for superfluous I/O accesses that can be optimized away, I stumbled upon this ACPI sleep I/O access and couldn't figure out why the hell this dummy op was necessary. After more than one hour of internet research, I had collected a sufficient number of documents (among those very old kernel versions) that finally told me what this dummy read was about: STPCLK# doesn't get asserted in time on (some) chipsets, which is why we need to have a dummy I/O read to delay further instruction processing until the CPU is fully stopped. Signed-off-by: NAndreas Mohr <andi@lisas.de> Signed-off-by: NLen Brown <len.brown@intel.com>
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