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

From: Pantelis Antoniou
Date: Fri Feb 20 2015 - 12:37:24 EST

Hi Rob,

> On Feb 20, 2015, at 19:30 , Rob Herring <robherring2@xxxxxxxxx> wrote:
> On Fri, Feb 20, 2015 at 8:35 AM, Ludovic Desroches
> <ludovic.desroches@xxxxxxxxx> 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@xxxxxxxxx> wrote:
>>>>> On 2/19/2015 9:00 AM, Pantelis Antoniou wrote:
>>>>>> Hi Frank,
> [...]
>>>>>> This is one of those things that the kernel community doesnât 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 youâre 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 itâs 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 youâre
>>>> 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 youâre 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 canât keep shoveling crap over
the fence to firmware and expect it to get buried there.

> Rob


â Pantelis

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