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Re: [PATCH] RM9000 serial driver

To: "Russell King" <>
Subject: Re: [PATCH] RM9000 serial driver
From: Thomas Koeller <>
Date: Wed, 30 Aug 2006 23:16:42 +0200
Cc: "Sergei Shtylyov" <>, "Yoichi Yuasa" <>,,,, Thomas Köller <>
In-reply-to: <>
Organization: Basler AG
Original-recipient: rfc822;
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On Tuesday 29 August 2006 21:04, Russell King wrote:
> It's worse than that - this code is there to read the ID from the divisor
> registers implemented in some UARTs.  If it isn't one of those UARTs, it's
> expected to return zero.
> So we don't actually want to be prodding some other random registers on
> differing UARTs.

For the  RM9000, DLL and DLM are located at distinct addresses, so these 
registers could be accessed without prior setting of DLAB. However, the
h/w docs say that DLAB has to be used nonetheless. I doubt that, but
wanted to play safe. So, in order to make this work, I had two options:

1. to monitor all register writes for setting/clearing of DLAB, and 
   switch the register mapping tables accordingly, or

2. implement serial_dl_read()/serial_dl_write() to directly access
   the registers, thus bypassing the mapping.

I decided to implement option #2, because it seemed less of a kludge.
Would you still say that this is an abuse?

Thomas Koeller, Software Development

Basler Vision Technologies
An der Strusbek 60-62
22926 Ahrensburg

Tel +49 (4102) 463-390
Fax +49 (4102) 463-46390

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