Re: 8250 UART doesn't work

[Woody Wu <narkewoody@gmail.com>]

On 2012-12-06, H. Peter Anvin <hpa@zytor.com> wrote:
> On 12/05/2012 11:56 PM, Woody Wu wrote:
>> Hi, list
>>
>> Does anyone here familiar to the serial 8250 driver?
>>
>> I enabled two uart ports in my board definition, but the ports doesn't
>> appear after I loaded the kernel (3.4.19).  I discovered, it failed at
>> the UART port auto configuration stage, the exact function is
>> autoconfig(...) in drivers/tty/serial/8250.c.
>>
>
> Sounds like you're using some kind of buggy UART IP... sharing which one 
> might help people identify the problem, if they have seen it before.
>
> 	-hpa
>

The UART controller is EXAR ST16C554D.  It claims as a 16550
compatible controller. Each ST16C554D module contains 4 UART, each of
them can be selected via two chip select pad. I think the board
hardware, via a CPLD, make the chip selection transparent to the CPU, so
by a 5-bit address, CPU can addressing individual 8 16550 compatible
registers of each UART.

I am not one hundred  percent sure I understood right, but this is all I
can say.  You experts can also judge whether this kind of hardware setup
is normal in embedded multi-serial ports solutions.

Many thanks!

-- 
woody
I can't go back to yesterday - because I was a different person then.