linux-kernel - Re: pch_uart and pch

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Message-ID: <CANKRQnhfQyUrMWaXJVsjmL-yFnHa9WuR5LfTkqv=QmRGnC2aTw@mail.gmail.com>
Date:	Fri, 17 Feb 2012 18:50:33 +0900
From:	Tomoya MORINAGA <tomoya.rohm@...il.com>
To:	Feng Tang <feng.tang@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>
Cc:	"lkml," <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, linux-serial@...r.kernel.org
Subject: Re: pch_uart and pch_phub clock selection

Hi

2012年2月17日16:28 Feng Tang <feng.tang@...el.com>:
> I see that the the CM-iTC board is special-cased to set a 192MHz uart_clock.
> This is done in pch_uart.c code, but there is some register manipulation done in
> the pch_phub.c driver and I don't understand the connection. How are the two
> related?
According to your use, need to configure clock registers which are in pch_phub .
Upstreamed version, UART_CLK can be used directly(neither multiple nor
division) as UART clock.

You can get clock configuration information from SourceForge.
(http://sourceforge.net/projects/ml7213/files/Kernel%202.6.37/Release/Ver1.2.0/EG20TPCH_ML7213_ML7223_ML7831_linux-2.6.37_v120_20110930.tar.bz2/
and extract pch_phub. you can find readme.)
I extract it and show below.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<Configuration>
=======================

1. Over 115K baud rate UART settings
    By default, UART can communicate less than 115Kbps.
    In case you want UART to work more than 115Kbps, the following
clock configuration is necessary.
    - Clock setting
          Set BAUDSEL = usb_48mhz
          Set PLL2VCO = "x 8" the clock
          Set BAUDDIV = "x 1/6" the clock
          Set UARTCLKSEL = PLL2 output
    For details, please refer to ML7213/ML7223 EDS "5 Chip Configuration"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In case we want UART to work high baud rate(e.g.4Mbps), we set like above.
and execute "setserial /dev/ttyPCH0 baud_base 4000000".
I can see PCH_UART with 4Mbps works well.

Darren, is this answer for your question ?

> Tomoya, do you know if we can also set it to 192MHz for ML7223 IOH Bus-m/n?
Yes, you can.

-- 
ROHM Co., Ltd.
tomoya
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