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Re: serial port 8250 messed up after coverting from little endian to big

To: "Florian Fainelli" <florian@openwrt.org>
Subject: Re: serial port 8250 messed up after coverting from little endian to big endian on kernel 2.6.31
From: myuboot@fastmail.fm
Date: Tue, 27 Oct 2009 15:40:13 -0500
Cc: linux-kernel@vger.kernel.org, "linux-mips" <linux-mips@linux-mips.org>
In-reply-to: <200910200817.24018.florian@openwrt.org>
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Thanks, Florian. I found the cause of the problem. My board is 32 bit
based, so each serial port register is 32bit even only 8 bit is used. So
when the board is switched endianess, I need to change the address
offset to access the same registers.
For example, original RHR register address is 0x8001000 with little
endian mode. With big endian, I need to access it as 0x8001003.

On Tue, 20 Oct 2009 08:17 +0200, "Florian Fainelli"
<florian@openwrt.org> wrote:
> Hi,
> 
> Le mardi 20 octobre 2009 01:56:04, myuboot@fastmail.fm a écrit :
> > I am trying to bringup a MIPS32 board using 2.6.31. It is working in
> > little endian mode. After changing the board's hardware from little
> > endian to bit endian, the serial port print messed up. It prints now
> > something like - "àààààààààààààààà" on the screen. When I trace the
> > execution, I can see the string the kernel is trying print is correct -
> > "Linux version 2.6.31 ..." and etc.
> > 
> > I guess it means the initialization of the serial port is not properly
> > done. But I am not sure where I should check for the problem. The serial
> > port device I am using is 8250. Please give me some advise.
> 
> If the same initialization routine used to work in little-endian, check
> how 
> you actually write and read characters from the UART FIFO and especially
> if 
> your hardware requires you to do word or byte access to these registers.
> 
> You can have a look at AR7, which has the same code working for Little
> and Big 
> Endian modes in arch/mips/ar7/prom.c lines 272 to the end of the file. It
> also 
> uses a 8250-compatible UART.

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