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Subject: Re: [PATCH v3] x86: i8237: Register based on FADT legacy boot flag
From:   Alan Cox <alan@linux.intel.com>
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Date:   Mon, 26 Mar 2018 15:55:16 +0100
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> Can we probe safely for this device?

99% of the time yes the inb gives us a straight answer. However (and
we've hit this with port 0x81 for real) there are concerns that some
systems will trap those addresses into SMM and do weirdness that makes
the 0xFF check fail.

Alan