linux-kernel - Possible bug in sc16is7xx UART driver

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Message-ID: <MW4PR09MB9284AF493E33E1E950361BAFEEC89@MW4PR09MB9284.namprd09.prod.outlook.com>
Date:   Mon, 23 Jan 2023 18:52:31 +0000
From:   "Wall, Stephen" <stephen.wall@...com.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Possible bug in sc16is7xx UART driver

I believe there is a bug in the startup function of the sc16is7xx driver code.  I've forked the repo and made changes with a descriptive comment here: https://github.com/torvalds/linux/commit/7a9c8f240efa4d3d49ab5b52ac1cfbe79a701acb

To summarize here, the data sheet for the part says that the MCR register can only be accessed when LCR[0] is cleared, and the function was attempting to access it with LCR set to 0xbf.

Note that I am not currently using linux, and don't have hardware to test this on.  I found it as a result of searching for code to compare with a local driver implementation on FreeBSD running on custom hardware.

Please CC me as I get failures when trying to subscribe to the list.