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

To: "Sergei Shtylyov" <sshtylyov@ru.mvista.com>, "Shmulik Ladkani" <jungoshmulik@gmail.com>
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: Wed, 28 Oct 2009 14:36:15 -0500
Cc: "Florian Fainelli" <florian@openwrt.org>, linux-kernel@vger.kernel.org, "linux-mips" <linux-mips@linux-mips.org>, shmulik@jungo.com
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Sergei, Shmulik,

Thanks a lot for your suggestions. I was using UPIO_MEM since I was not
aware of the difference between UPIO_MEM and UPIO_MEM32. 

I just tried UPIO_MEM32 without adding a offset of 3. But the result is
bad - after the kernel initializes the serial console, the console print
out messes up. The early printk is fine because the u-boot initialises
the serial port fine. 

How I tried UPIO_MEM32 is in platform.c changing the iotype to
UPIO_MEM32 in the uart_port structure and passing the structure to
early_serial_setup. What I did is  the same as in
arch/mips/ar7/platform.c.

In 8250.c I removed the offset I added to mem_serial_out and
mem_serial_in. 
Did I miss anything? Thanks again for your help.

On Wed, 28 Oct 2009 14:04 +0300, "Sergei Shtylyov"
<sshtylyov@ru.mvista.com> wrote:
> Hello.
> 
> Shmulik Ladkani wrote:
> 
> >> 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.
> >>     
> >
> > I assume your uart_port's iotype is defined as UPIO_MEM32.
> >   
> 
>    He wouldn't have to add 3 to the register addresses then.
> 
> > UPIO_MEM32 makes 8250 access serial registers using readl/writel (which 
> > might
> > be a problem for big-endian), while UPIO_MEM makes 8250 access the registers
> > using readb/writeb.
> >   
> 
>    Both may be a problem for big endian.
> 
> > Maybe you should try UPIO_MEM (assuming hardware allows byte access).
> 
>    Contrarywise, I think he now has UPIO_MEM and needs to try UPIO_MEM32.
> 
> WBR, Sergei
> 
> 

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