linux-kernel - Re: [PATCH v7] serial: support for 16550A serial ports on LP-8x4x

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Message-ID: <20160301184327.148b3ad4@lxorguk.ukuu.org.uk>
Date:	Tue, 1 Mar 2016 18:43:27 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Sergei Ianovich <ynvich@...il.com>, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Paul Burton <paul.burton@...tec.com>,
	Mans Rullgard <mans@...sr.com>,
	Joachim Eastwood <manabian@...il.com>,
	Scott Wood <scottwood@...escale.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@...r.kernel.org>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v7] serial: support for 16550A serial ports on LP-8x4x

> Maybe you just set a baud rate nearest to the one from the table in
> case of BOTHER?

This is broken. BOTHER can be set with a perfectly valid baud rate that
could equally be represented by B9600 say.

If you are stuck with limited ranges then

	switch(baud) {
	case 9600:
	case 4800:

etc

and don't worry about BOTHER, it's entirely transparent to you. The core
kernel code will provide you with a baud rate number, the re-encoder will
always do the right thing.

A driver should never care about BOTHER or any of the baud bits in the
termios structure directly.

Alan