From mboxrd@z Thu Jan  1 00:00:00 1970
From: cyril@ti.com (Cyril Chemparathy)
Date: Fri, 30 Apr 2010 12:20:35 -0400
Subject: [PATCH 02/14] omap: Make uncompress code and DEBUG_LL code generic
In-Reply-To: <1272640022.3051.1534.camel@localhost>
References: <20100126200646.15382.52167.stgit@baageli.muru.com>	
	<20100126201239.15382.34792.stgit@baageli.muru.com>
	<1272640022.3051.1534.camel@localhost>
Message-ID: <4BDB0353.5090800@ti.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi,

[...]
> To fix both problems, maybe we should just use a fixed memory location
> to pass this temporary data from uncompress to the kernel.  We've had a
> similar problem on DaVinci recently and a proposal has been made (and
> tested) to use memory just below the page tables[3].)

Essentially both of these approaches (internal scratch register and
fixed address) implement a weird back-channel communication scheme
between the decompresser and the debug macros.

A more elegant solution may be as follows:
    - pass machine_arch_type as an argument into addruart.
    - move the uart base lookup logic to addruart using macros similar
      to DEBUG_LL_*, except that these expand to assembly code this
      time.
    - reuse these debug-macros in uncompress.h and implement putc() and
      flush() using addruart(), senduart(), etc.

This way, both the decompresser and the kernel debug macros end up using
machine_arch_type to get to the right debug uart, without resorting to
underhand back-channel tricks.

Any thoughts?

-- Cyril.