linux-kernel - Re: [PATCHv3 2/7] ARM: at91: introduce basic SAMA5D4 support

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Date:	Fri, 26 Sep 2014 16:54:53 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/7] ARM: at91: introduce basic SAMA5D4 support

Hi Alexandre,

On Fri, 2014-09-26 at 16:13 +0200, Alexandre Belloni wrote:
> On 26/09/2014 at 13:47:03 +0200, Paul Bolle wrote :
> > On Mon, 2014-09-15 at 18:15 +0200, Alexandre Belloni wrote:
> > > From: Nicolas Ferre <nicolas.ferre@...el.com>
> > > 
> > > Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>
> > 
> > This landed in next-20140926, as commit 2dc850b62e5b ("ARM: at91:
> > introduce basic SAMA5D4 support").
> > 
> > > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> > > index b11ad54f8d17..7b44db208f10 100644
> > > --- a/arch/arm/Kconfig.debug
> > > +++ b/arch/arm/Kconfig.debug
> > > @@ -101,6 +101,10 @@ choice
> > >  		bool "Kernel low-level debugging on 9263 and 9g45"
> > >  		depends on HAVE_AT91_DBGU1
> > >  
> > > +	config AT91_DEBUG_LL_DBGU2
> > > +		bool "Kernel low-level debugging on sama5d4"
> > > +		depends on HAVE_AT91_DBGU2
> > > +
> > 
> > Why is this Kconfig symbol needed? Nothing in next-20140926 uses it. Are
> > future users perhaps queued somewhere (say, in commits that didn't
> > survive today's rather lively linux-next merges)? 
> 
> There is no user because it conflicts with the previous one that is
> selected by default by the sama5_defconfig. This is for early print and
> it means that you can get earlyprintk either for sama5d3 or sama5d4.
> 
> My guess is that it will never be included in any defconfig.

I missed that this is inside a "choice" (which complicates matters quite
a bit)!

There are a number of cases where one of the configs inside the choice
only serve to _not_ set anything. In those cases the Kconfig symbol is
used nowhere else. I'll have to think about this particular symbol a bit
more to see if it actually makes sense to not use it anywhere else.

Thinking about the "Kernel low-level debugging port" choice is
complicated by the fact that it holds about a gazillion "config"
entries, many of which only show up only if some dependency is met. So
it might take me some time to say anything sensible about it, if I ever
manage to do that at all...

Thanks,


Paul Bolle

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