[U-Boot-Users] using a flat device tree to drive u-boot config

[André Schwarz]

Wolfgang Grandegger schrieb:
> André Schwarz wrote:
>> Ben Warren schrieb:
>>> On Mon, Jul 28, 2008 at 10:43 AM, Scott Wood 
>>> <scottwood at freescale.com> wrote:
>>>> Ben Warren wrote:
>>>>> On Mon, Jul 28, 2008 at 10:32 AM, Scott Wood <scottwood at freescale.com>
>>>>> wrote:
>>>>>> I find a device tree much easier to figure out than a tangled mess of
>>>>>> header
>>>>>> files, #defines, and #ifdefs...
>>>>> In many ways, yes.  But are you an average Joe or a Linux kernel
>>>>> propellerhead?
>>>> Is u-boot work normally done by average Joes, and does the average Joe
>>>> really find the preprocessor mess more intuitive than a 
>>>> "propellerhead"?
>>>>
>>> You know what I mean.  Some people like yourself do this for a living,
>>> and are involved day-to-day in its specification.  Of course it's
>>> intuitive to you.  For most people, getting U-boot going is one stage
>>> in the development process of software for an embedded device.  They
>>> work on it for a few weeks or months, then on something completely
>>> different.  A few months or years later, they come back to it.
>>
>> You're absolutely right - just have a look at the vast lists of 
>> maintainers/contributors ... they are "average Joes" like myself. 
>> Realizing 2-3 projects each year should be possible without having to 
>> re-learn from scratch.
>>
>>>> While we're at it, let's re-write u-boot in Visual Basic. :-)
>>> Uh, yeah.  I like the idea of a central repo for hardware info, and
>>> the device tree concept is good.  My point is that the syntax, while
>>> concise and exact, can be intimidating.  Just look at the amount of
>>> traffic on the mailing lists of people that don't understand what all
>>> the fields mean when specifying IRQs etc.  Anything we can do to make
>>> it less so for noobies is a good thing for everybody.
>>>
>>
>> Please keep in mind that WDenk is always watching if code is slowing 
>> things down or increasing size significantly. Improving things is very 
>> good - but not at the cost of size and/or speed. Configuring a board 
>> using a dtb usually needs far more code being present than needed.
>> After all it's a bootloader and not another pseudo OS.
>>
>> But don't get me wrong ! The device tree is a very nice and usefuly 
>> thing ... for an OS.
> 
> There are customer request for a dynamically configurable U-Boot and the 
> FDT is the right tool to provide the functionality. It has its price but 
> U-Boot using a FDT blob for booting would also save some fixup code 
> (required to boot Linux) and furthermore it would resolves some 
> dependencies between hardcoded U-Boot and FDT defined addresses and ranges.
> 

yes of course ... if you're thinking about paying customers.

What I can _definitely_ say is that we had to change flash layout twice 
on *existing* products simply because bootloader and kernel are 
constantly growing. It's nearly impossible to keep it small ... even 
with same core functionality.

Only way out would be to freeze versions. That's what lots of companies 
are doing ... and this is why so many out-of-tree branches exist. But 
that's another topic ;-)

regards,
André

> Wolfgang.


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