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

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Date:	Fri, 6 Dec 2013 13:42:11 +1100
From:	James Cameron <quozl@...top.org>
To:	Sergei Ianovich <ynvich@...il.com>
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, Dec 06, 2013 at 03:28:37AM +0400, 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.

[...]

> +/* 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.

I did not check the other errata work arounds.

--
James Cameron
http://quozl.linux.org.au/
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