Re: [PATCH v3 4/6] arm: add basic support for Mediatek MT6589 boards

[Rob Herring <robherring2@gmail.com>]

On Wed, May 14, 2014 at 2:00 AM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> Hi Stephen,
>
> On Tue, May 13, 2014 at 03:47:32PM -0700, Stephen Boyd wrote:
>> On 05/13, Matthias Brugger wrote:
>> > diff --git a/arch/arm/mach-mediatek/mediatek.c b/arch/arm/mach-mediatek/mediatek.c
>> > new file mode 100644
>> > index 0000000..73dfb05
>> > --- /dev/null
>> > +++ b/arch/arm/mach-mediatek/mediatek.c
>> > @@ -0,0 +1,32 @@
>> > +/*
>> > + * Device Tree support for Mediatek SoCs
>> > + *
>> > + * Copyright (c) 2014 MundoReader S.L.
>> > + * Author: Matthias Brugger <matthias.bgg@gmail.com>
>> > + *
>> > + * 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.
>> > + *
>> > + * This program is distributed in the hope that it will be useful,
>> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> > + * GNU General Public License for more details.
>> > + */
>> > +
>> > +#include <linux/kernel.h>
>> > +#include <linux/init.h>
>> > +#include <linux/of_platform.h>
>> > +#include <linux/irqchip.h>
>> > +#include <asm/mach/arch.h>
>> > +#include <asm/mach/map.h>
>> > +
>> > +static const char * const mediatek_board_dt_compat[] = {
>>
>> __initconst?
>>
>> > +   "mediatek,mt6589",
>> > +   NULL,
>> > +};
>> > +
>> > +DT_MACHINE_START(MEDIATEK_DT, "Mediatek Cortex-A7 (Device Tree)")
>> > +   .dt_compat      = mediatek_board_dt_compat,
>> > +MACHINE_END
>>
>> You shouldn't need this file at all if the platform is part of
>> the multi-platform kernel.
>
> From a technical point of view, you don't. But it's interesting to
> keep it mostly for two things:
>   - You get to see the platform name in /proc/cpuinfo

We should be getting this string from model or top-level compatible
string in the dtb. I did a patch to do just this [1], but people did
not like removing this string. We should really decide if getting rid
of machine descriptors is a goal or not.

We should at least make things such that the cpuinfo string does not
change on new platforms based on whether they have a machine desc or
not.

>   - If you ever need to add platform quirks, it's already there

That is a weak argument when usually we add things as they are needed.

Rob

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-November/208878.html