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

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Date:	Tue, 01 Mar 2016 22:28:13 +0300
From:	Sergei Ianovich <ynvich@...il.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Cc:	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	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

On Tue, 2016-03-01 at 19:48 +0200, Andy Shevchenko wrote:
> On Tue, 2016-03-01 at 20:14 +0300, Sergei Ianovich wrote:
> > On Tue, 2016-03-01 at 18:46 +0200, Andy Shevchenko wrote:
> > > On Tue, 2016-03-01 at 19:25 +0300, Sergei Ianovich wrote:
> > > > On Tue, 2016-03-01 at 13:06 +0200, Andy Shevchenko wrote:
> > > > > On Tue, 2016-03-01 at 00:26 +0300, Sergei Ianovich wrote:
> 
> > > So, but if you support only fixed rates, why do you care about
> > > BOTHER
> > > at all?
> > 
> > If BOTHER is defined, tty_termios_baud_rate()
> > and tty_termios_encode_baud_rate() allow non-standard baud rates. I
> > should clear it from c_cflag to indicate I don't support it.
> > 
> > > > > >  
> > > > > I think you can call this unconditionally together with case
> > > > > >
> > > > > 115200.
> > > > 
> > > > The calls are orthogonal. This one deals with the case when
> > > > BOTHER
> > > > is
> > > > defined and set, and we have non-zero rate with BOTHER, but we
> > > > have
> > > > zero rate after BOTHER is cleared. So we set 9600 as a sane
> > > > default
> > > > speed.
> 
> Maybe you just set a baud rate nearest to the one from the table in
> case of BOTHER?
> 
> In that case perhaps you have to supply +-1 to the range. That's why
> I
> asked about uart_get_baud_rate(). 
> 
> Maybe this flow will work for you
> 
> if (BOTHER)
>  clear BOTHER
>  call uart_get_baud_rate()
> 
> ?

It works well for standard rates, let it be so. If there ever is a
problem, we can fix it.