linux-kernel - Re: [PATCH] arm: choose debug/uncompress.h include when uncompress debug is disabled

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Message-ID: <20130717151816.GN24642@n2100.arm.linux.org.uk>
Date:	Wed, 17 Jul 2013 16:18:16 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	Arnd Bergmann <arnd@...db.de>, patches@...aro.org,
	Julien Grall <julien.grall@...aro.org>,
	linux-kernel@...r.kernel.org, Olof Johansson <olof@...om.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm: choose debug/uncompress.h include when uncompress
	debug is disabled

On Wed, Jul 17, 2013 at 04:11:48PM +0100, Russell King - ARM Linux wrote:
> On Wed, Jul 17, 2013 at 02:25:38PM +0100, Stefano Stabellini wrote:
> > On Mon, 15 Jul 2013, Julien Grall wrote:
> > > Even if uncompress debug is disabled, some board will continue to print
> > > information during uncompress step.
> > 
> > Are you talking about DEBUG_UNCOMPRESS?
> > Should I read the sentence as "even if DEBUG_UNCOMPRESS is not selected,
> > some board will continue to print information during the uncompress step"?
> > 
> > Isn't this a bug in the platform specific code that should be fixed anyway?
> 
> Hang on, let's be clear what's going on here.
> 
> 1. The normal output from the decompressor is *not* debugging.  By that
>    I mean the "Uncompressing kernel... done" message.  That is part of
>    user output.
> 
> 2. In non-multiplatform environments, the decompressor will normally use
>    the putc/flush functions found in arch/arm/mach-*/include/mach/uncompress.h
>    to implement its output, irrespective of the DEBUG_UNCOMPRESS setting.
>    (An interesting point is that DEBUG_UNCOMPRESS really should depend on
>    MULTIPLATFORM so that this point is explicit - the option requires
>    MULTIPLATFORM to be set.)
> 
> 3. DEBUG_UNCOMPRESS allows the functions which we've implemented for LL
>    debug to be re-used for decompressor output.
> 
> 4. When DEBUG_UNCOMPRESS is not set in a multiplatform kernel, the
>    decompressors putc() and flush() functions are stubbed out.
> 
> So, it's quite right that you get output from the decompressor even when
> DEBUG_UNCOMPRESS is not set.  There's no problem with that.

Does this patch help to explain this?

 arch/arm/Kconfig.debug |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index e401a76..583f4a0 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -804,9 +804,19 @@ config DEBUG_LL_INCLUDE
 
 config DEBUG_UNCOMPRESS
 	bool
-	default y if ARCH_MULTIPLATFORM && DEBUG_LL && \
-		     !DEBUG_OMAP2PLUS_UART && \
+	depends on ARCH_MULTIPLATFORM
+	default y if DEBUG_LL && !DEBUG_OMAP2PLUS_UART && \
 		     !DEBUG_TEGRA_UART
+	help
+	  This option influences the normal decompressor output only for
+	  multiplatform kernels.  Normally, multiplatform kernels disable
+	  decompressor output because it is not possible to know where to
+	  send the decompressor output.
+
+	  When this option is set, the selected DEBUG_LL output method
+	  will be re-used for normal decompressor output on multiplatform
+	  kernels.
+	  
 
 config UNCOMPRESS_INCLUDE
 	string
--
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