linux-kernel - Re: [PATCH 2/4] of: DT quirks infrastructure

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Message-Id: <37628878-C4B4-49F6-9000-B993250F54AB@konsulko.com>
Date:	Fri, 20 Feb 2015 19:37:08 +0200
From:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Frank Rowand <frowand.list@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Matt Porter <matt.porter@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Ludovic Desroches <ludovic.desroches@...el.com>
Subject: Re: [PATCH 2/4] of: DT quirks infrastructure

Hi Rob,

> On Feb 20, 2015, at 19:30 , Rob Herring <robherring2@...il.com> wrote:
> 
> On Fri, Feb 20, 2015 at 8:35 AM, Ludovic Desroches
> <ludovic.desroches@...el.com> wrote:
>> On Fri, Feb 20, 2015 at 09:21:38AM -0500, Peter Hurley wrote:
>>> On 02/19/2015 12:38 PM, Pantelis Antoniou wrote:
>>>> 
>>>>> On Feb 19, 2015, at 19:30 , Frank Rowand <frowand.list@...il.com> wrote:
>>>>> 
>>>>> On 2/19/2015 9:00 AM, Pantelis Antoniou wrote:
>>>>>> Hi Frank,
> 
> [...]
> 
>>>>>> This is one of those things that the kernel community doesn’t understand which makes people
>>>>>> who push product quite mad.
>>>>>> 
>>>>>> Engineering a product is not only about meeting customer spec, in order to turn a profit
>>>>>> the whole endeavor must be engineered as well for manufacturability.
>>>>>> 
>>>>>> Yes, you can always manually install files in the bootloader. For 1 board no problem.
>>>>>> For 10 doable. For 100 I guess you can hire an extra guy. For 1 million? Guess what,
>>>>>> instead of turning a profit you’re losing money if you only have a few cents of profit
>>>>>> per unit.
>>>>> 
>>>>> I'm not installing physical components manually.  Why would I be installing software
>>>>> manually?  (rhetorical question)
>>>>> 
>>>> 
>>>> Because on high volume product runs the flash comes preprogrammed and is soldered as is.
>>>> 
>>>> Having a single binary to flash to every revision of the board makes logistics considerably
>>>> easier.
>>>> 
>>>> Having to boot and tweak the bootloader settings to select the correct dtb (even if it’s present
>>>> on the flash medium) takes time and is error-prone.
>>>> 
>>>> Factory time == money, errors == money.
>>>> 
>>>>>> 
>>>>>> No knobs to tweak means no knobs to break. And a broken knob can have pretty bad consequences
>>>>>> for a few million units.
>>>>> 
>>>>> And you produce a few million units before testing that the first one off the line works?
>>>>> 
>>>> 
>>>> The first one off the line works. The rest will get some burn in and functional testing if you’re
>>>> lucky. In many cases where the product is very cheap it might make financial sense to just ship
>>>> as is and deal with recalls, if you’re reasonably happy after a little bit of statistical sampling.
>>>> 
>>>> Hardware is hard :)
>>> 
>>> I'm failing to see how this series improves your manufacturing process at all.
>>> 
>>> 1. Won't you have to provide the factory with different eeprom images for the
>>>   White and Black?  You _trust_ them to get that right, or more likely, you
>>>   have process control procedures in place so that you don't get 1 million Blacks
>>>   flashed with the White eeprom image.
>>> 
>>> 2. The White and Black use different memory technology so it's not as if the
>>>   eMMC from the Black will end up on the White SMT line (or vice versa).
>>> 
>>> 3  For that matter, why wouldn't you worry that all the microSD cards intended
>>>   for the White were accidentally assembled with the first 50,000 Blacks; at
>>>   that point you're losing a lot more than a few cents of profit. And that has
>>>   nothing to do with what image you provided.
>>> 
>> 
>> As you said, we can imagine many reasons to have a failure during the
>> production, having several DTB files will increase the risk.
> 
> Then package them as a single file. You can even use DT to do that.
> See u-boot FIT image.
> 

In the ideal case there is no u-boot, and no bootloader.

Packaging 27 difference DTBs, as in the Atmel people case, differing in only a few 
properties seems a waste of space, no?  

We keep on dancing around the issue, namely that DT does not have a quirk/variant
mechanism. I feel that it is a glaring omission. We can’t keep shoveling crap over
the fence to firmware and expect it to get buried there.

> Rob

Regards

— Pantelis

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