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

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Message-ID: <6ae4dd827bf4dcc202f60e8505173d0e@agner.ch>
Date:	Wed, 17 Dec 2014 00:41:33 +0100
From:	Stefan Agner <stefan@...er.ch>
To:	Arnd Bergmann <arnd@...db.de>
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 2014-12-03 12:03, Arnd Bergmann wrote:
> On Wednesday 03 December 2014 01:12:10 Stefan Agner wrote:
>> diff --git a/arch/arm/boot/dts/vf610m4-colibri.dts b/arch/arm/boot/dts/vf610m4-colibri.dts
>> new file mode 100644
>> index 0000000..051ee0f
>> --- /dev/null
>> +++ b/arch/arm/boot/dts/vf610m4-colibri.dts
>> @@ -0,0 +1,52 @@
>> +/*
>> + * Device tree for Colibri VF61 Cortex-M4 support
>> + *
>> + * Copyright 2014 Stefan Agner
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + */
>> +
>> +/dts-v1/;
>> +#include "vf610m4.dtsi"
>> +
>> +/ {
>> +       model = "VF610 Cortex-M4";
>> +       compatible = "fsl,vf610m4";
>> +
>> +       chosen {
>> +               bootargs = "console=ttyLP2,115200 ihash_entries=64 dhash_entries=64 earlyprintk clk_ignore_unused init=/linuxrc rw";
>> +       };
>> +
> 
> Starting with v3.19, you should be able to use the earlycon framework on
> arm32, so it would be better to replace earlyprintk with earlycon here
> and add a stdout-path property in chosen that points to the console
> uart.

I started to implement earlycon support, but something currently fails
when earlycon tries to map the UART registers:
[    0.000000] earlycon_map: Couldn't map 0x40027000

I traced the issue a bit further down and found that get_vm_area_caller
returns NULL (in __arm_ioremap_pfn_caller). This happend on Linus master
as of today (2dbfca5a181973558277b28b1f4c36362291f5e0). Do I miss
something here?

> 
> 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.
> 
> 	Arnd

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