linux-kernel - Re: serial port 8250 messed up after coverting from little endian to big endian on kernel 2.6.31

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Message-ID: <4AE82520.4090607@ru.mvista.com>
Date:	Wed, 28 Oct 2009 14:04:00 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Shmulik Ladkani <jungoshmulik@...il.com>
Cc:	myuboot@...tmail.fm, Florian Fainelli <florian@...nwrt.org>,
	linux-kernel@...r.kernel.org,
	linux-mips <linux-mips@...ux-mips.org>, shmulik@...go.com
Subject: Re: serial port 8250 messed up after coverting from little endian
 to big endian on kernel  2.6.31

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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