linux-kernel - Re: [PATCH 11/12] ARM: dts: add support for Vybrid running on Cortex-M4

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Date:	Wed, 17 Dec 2014 11:57:06 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Stefan Agner <stefan@...er.ch>
Cc:	linux-arm-kernel@...ts.infradead.org, shawn.guo@...aro.org,
	kernel@...gutronix.de, linux@....linux.org.uk,
	u.kleine-koenig@...gutronix.de, jason@...edaemon.net,
	olof@...om.net, daniel.lezcano@...aro.org, tglx@...utronix.de,
	mark.rutland@....com, pawel.moll@....com, robh+dt@...nel.org,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/12] ARM: dts: add support for Vybrid running on Cortex-M4

On Tuesday 16 December 2014 23:19:08 Stefan Agner wrote:
> On 2014-12-03 12:03, Arnd Bergmann wrote:
> > On Wednesday 03 December 2014 01:12:10 Stefan Agner wrote:

> Just started looking in that a bit deeper and some question arose:
> Afaik, earlycon need to be supported by the uart driver. The fsl_lpuart,
> which is used for Vybrid's uart, does not support earlycon yet. However,
> earlyprink already works (see ./arch/arm/include/debug/vf.S). I
> understand that earlycon has the advantage of being able to be used on
> multiplatform. But earlyprintk is working really early (e.g. before
> locating the FDT), and it proved helpful for me when I started working
> on that Cortex-M4 stuff. Should earlycon replace earlyprintk completely?

earlyprintk will stay around for debugging early boot problems, but
with working earlycon support, there should no longer be a reason to
enable it by default.

> Maybe, on Vybrid, since it would be a good platform for automated !MMU
> testing, it would be nice to have earlycon which can be enabled in any
> case and would provide output even something blows up quite early... But
> I guess I would add earlycon support as part of a new patchset and just
> drop earlyprintk here for now.

Yes, I think that would be good.

> > 64 hash table entries sounds extremely small, doesn't that impact
> > performance? If you have 50MB of actual RAM available, I don't think
> > you need that.
> 
> Agreed. I copied that from EFM32 which is under much more memory
> pressure...

Ok.
	
	Arnd
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