linux-kernel - Re: [RFC][PATCH] Xilinx uartlite serial driver

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Date:	Wed, 13 Sep 2006 07:56:03 +0200
From:	Peter Korsgaard <jacmet@...site.dk>
To:	Olof Johansson <olof@...om.net>
Cc:	rmk+serial@....linux.org.uk, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Xilinx uartlite serial driver

>>>>> "Olof" == Olof Johansson <olof@...om.net> writes:

Hi Olof, thanks for looking into the driver..

 Olof> In my opinion there's a few pieces missing:

 Olof> 1. There's no early boot console support for PPC. There's another
 Olof> uartlite patch that's floating around that has this, very useful for
 Olof> early bringup tasks. I'd like to see this expanded to include that as
 Olof> well (the regular part of the other driver seems more or less broken
 Olof> though, so this is a better base driver). That shouldn't stop this part
 Olof> of the driver to go in though, just possible future work.

True. The board I have an uartlite on also has a 8250 so it hasn't
been an issue for me so far - But it would indeed be a nice
addition. Adding new stuff to arch/ppc at this moment isn't that
sensible, so perhaps it makes most sense to wait til 4xx is supported
under arch/powerpc?

 Olof> 2. There seems to be some timeout issues with tx_empty. If I boot a
 Olof> regular distro with getty, etc, I get veeeery slow console output right
 Olof> when init starts up. Adding a small default timeout in the init of the
 Olof> uart code seems to help -- the hanging thread seems to be sleeping in
 Olof> uart_wait_until_sent(). I picked a value of '5', seems ok. (Also,
 Olof> without this fix, getty won't start on the port for some reason, it
 Olof> sits in the same timeout forever, or at least for a very long time).

Huh, that's odd - I haven't noticed that. I'll test it again and get
back to you.

 Olof> 3. It would be useful to demonstrate how to hook up the device all the
 Olof> way through to the board port (i.e. add a config option and include it
 Olof> in the ml403 platform code or similar). It's not hard, but it'd make it
 Olof> easier for whomever comes next. Of course, with 4xx hopefully soon
 Olof> moving over to arch/powerpc, this would be taken care of through the
 Olof> device tree instead.

Yes - Afaik none of the Xilinx boards comes with uartlites
configured so it's not usable out-of-the-box, but you can ofcause do a
setup with the proper #ifdefs like the 8250 stuff in virtex.c.

-- 
Bye, Peter Korsgaard
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