linux-kernel - Re: [PATCH 1/1] ARM: dts: zynq: Add Parallella device tree

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Date:	Tue, 15 Jul 2014 12:53:56 +0200
From:	Michal Simek <michal.simek@...inx.com>
To:	Olof Johansson <olof@...om.net>,
	Michal Simek <michal.simek@...inx.com>
CC:	Andreas Färber <afaerber@...e.de>,
	Andreas Olofsson <andreas@...pteva.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 1/1] ARM: dts: zynq: Add Parallella device tree

On 07/14/2014 08:12 PM, Olof Johansson wrote:
> On Tue, Jul 8, 2014 at 4:18 AM, Michal Simek <michal.simek@...inx.com> wrote:
>> On 06/30/2014 07:15 AM, Olof Johansson wrote:
>>> Hi,
>>>
>>> On Sun, Jun 29, 2014 at 1:50 PM, Andreas Färber <afaerber@...e.de> wrote:
>>>> This allows to boot the Adapteva Parallella board to serial console.
>>>>
>>>> Cc: Andreas Olofsson <andreas@...pteva.com>
>>>> Signed-off-by: Andreas Färber <afaerber@...e.de>
>>>
>>> Nice and clean DTS, just a couple of comments below.
>>>
>>>> diff --git a/arch/arm/boot/dts/zynq-parallella.dts b/arch/arm/boot/dts/zynq-parallella.dts
>>>> new file mode 100644
>>>> index 0000000..98df66c
>>>> --- /dev/null
>>>> +++ b/arch/arm/boot/dts/zynq-parallella.dts
>>>> @@ -0,0 +1,63 @@
>>>> +/*
>>>> + * Copyright (c) 2014 SUSE LINUX Products GmbH
>>>> + *
>>>> + * Derived from zynq-zed.dts:
>>>> + *
>>>> + *  Copyright (C) 2011 Xilinx
>>>> + *  Copyright (C) 2012 National Instruments Corp.
>>>> + *  Copyright (C) 2013 Xilinx
>>>> + *
>>>> + * This software is licensed under the terms of the GNU General Public
>>>> + * License version 2, as published by the Free Software Foundation, and
>>>> + * may be copied, distributed, and modified under those terms.
>>>> + *
>>>> + * 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.
>>>> + */
>>>> +/dts-v1/;
>>>> +/include/ "zynq-7000.dtsi"
>>>> +
>>>> +/ {
>>>> +       model = "Parallella Board";
> 
> You might want to have this say "Adapteva Parallella Board" instead
> (just noticed).
> 
>>>> +       compatible = "xlnx,zynq-7000";
>>>
>>> This should have a more specific compatible as the first one. Probably
>>> something like:
>>>    compatible = "adapteva,parallella", "xlnx,zynq-7000";
>>
>> We were using these compatible properties but later there is no reason
>> to create them because they will be unused.
>> It is easy to add it when you need it which is not this case.
> 
> No, please add it from day one, otherwise everybody needs to update
> their device tree, some will miss doing it, etc, etc. It's a simple
> and trivial thing to do, and no reason to leave it o ut.

It is trivial. None will just probably use it and upgrading DTS is simple
but I don't really care.


>>>> +
>>>> +       memory {
>>>> +               device_type = "memory";
>>>> +               reg = <0 0x20000000>;
>>>
>>> Does the bootloader update this entry, or is it truly static? If it's
>>> updated then it's become recent habit to leave the memory size empty
>>> in the static file.
>>
>> Depends on your bootloader. I think it is good to have it here.
>> Also this file can be used by u-boot for example and u-boot can be configured
>> from it that's why I think that make sense to keep this here.
> 
> Ok. It's become commonplace to leave memory empty for the machines
> where it's guaranteed that the bootloader will have updated it, to
> avoid having stale or incorrect values in the static tree. I'm not
> going to be strict about it, but it's something to consider.

I personally don't like this bootloader feature and IRC it is disabled
for xilinx u-boot too.

Thanks,
Michal



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