linux-kernel - Re: [PATCH v6] serial: rewrite pxa2xx-uart to use 8250

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Message-ID: <1456106191.2386.13.camel@gmail.com>
Date:	Mon, 22 Feb 2016 04:56:31 +0300
From:	Sergei Ianovich <ynvich@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	James Cameron <quozl@...top.org>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Russell King <linux@....linux.org.uk>,
	Jiri Slaby <jslaby@...e.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Joachim Eastwood <manabian@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Scott Wood <scottwood@...escale.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Paul Burton <paul.burton@...tec.com>,
	Mans Rullgard <mans@...sr.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v6] serial: rewrite pxa2xx-uart to use 8250_core

On Sat, 2016-02-06 at 22:22 -0800, Greg Kroah-Hartman wrote:
> On Thu, Dec 24, 2015 at 06:15:14PM +0300, Sergei Ianovich wrote:
> > pxa2xx-uart was a separate uart platform driver. It was declaring
> > the same device names and numbers as 8250 driver. As a result,
> > it was impossible to use 8250 driver on PXA SoCs.
> > 
> > Upon closer examination pxa2xx-uart turned out to be a clone of
> > 8250_core driver.
> > 
> > Workaround for Erratum #19 according to Marvel(R) PXA270M Processor
> > Specification Update (April 19, 2010) is dropped. 8250_core reads
> > from FIFO immediately after checking DR bit in LSR.
> > 
> > The patch leaves the original SERIAL_PXA driver around. The
> > original
> > driver is just marked DEPRECATED in Kconfig and C source. When
> > the original driver is considered safe to remove, no changes
> > to SERIAL_8250 will be necessary.
> 
> But, you just broke existing configurations, right?  The serial port is
> a different name now, are you willing to handle the angry users?

No, the port name remains /dev/ttyS0. In fact, this conflict (both
drivers use the same name and char major) is the reason for the patch.
Noone should notice the change at runtime. There will be a warning at
compile time which should make the transition to the new driver faster.

> If so, great, get the platform maintainer to sign off on this please and
> then resend it.

The previous version of the patch has been around for 2 years with half
a dozen of Acks and Reviews, but it hasn't landed. Could you suggest a
better approach?

-- 
Sergei Ianovich <ynvich@...il.com>