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

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Date:	Fri, 06 Dec 2013 13:16:52 +0400
From:	Sergei Ianovich <ynvich@...il.com>
To:	James Cameron <quozl@...top.org>
Cc:	linux-kernel@...r.kernel.org,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Crispin <blogic@...nwrt.org>, Jiri Slaby <jslaby@...e.cz>,
	"moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
	Zhou Zhu <zzhu3@...vell.com>
Subject: Re: [PATCH] serial: rewrite pxa2xx-uart to use 8250_core

On Fri, 2013-12-06 at 13:42 +1100, James Cameron wrote:
> On Fri, Dec 06, 2013 at 03:28:37AM +0400, Sergei Ianovich wrote:
> > +/* Uart divisor latch write */
> > +static void serial_pxa_dl_write(struct uart_8250_port *up, int value)
> > +{
> > +	serial_out(up, UART_DLL, value & 0xff);
> > +	serial_out(up, UART_DLM, value >> 8 & 0xff);
> > +}
> 
> This is a change.  drivers/tty/serial/pxa.c did read back UART_DLL as
> an errata work around:
> 
> > -	/*
> > -	 * work around Errata #75 according to Intel(R) PXA27x Processor Family
> > -	 * Specification Update (Nov 2005)
> > -	 */
> > -	dll = serial_in(up, UART_DLL);
> > -	WARN_ON(dll != (quot & 0xff));
> 
> If this is no longer needed, serial_pxa_dl_write can be removed
> because it is same as default_serial_dl_write.

Thanks for spotting this. I prepared infrastructure, but the tests never
failed so I never returned here. I've filed v2 with correct dl_write.

> I did not check the other errata work arounds.

I've intentionally dropped workaround for E20 from old pxa.c
receive_chars(). 8250_core reads FIFO immediately after it checks DR bit
in LSR, so that issue never happens. New version states this in commit
message.

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