Handling of modular boards
swarren at wwwdotorg.org
Fri May 4 17:09:19 EDT 2012
On 05/04/2012 03:03 PM, Arnd Bergmann wrote:
> On Friday 04 May 2012, Wolfgang Denk wrote:
>> There are systems (and I bet it will be a growing number) where U-Boot
>> itself uses the DT for configuration. Also, there are functions that
>> are needed both by the boot loader and the kernel - for example to
>> dislay a splash screen the boot loader needs to initialize the
>> display, so it must be able to detect which type of LCD is attached
>> (resolution, color-depth, orientation) - the device tree comes in very
>> handy here. Why should Linux re-do all such things?
> Sure, there are a lot of things that the boot loader can use from the
> device tree, but I'm not sure if the LCD panel connection fits into
> the same category as the devices that Mark was thinking of.
A board I have sitting on my desk right now has separate boards for (and
multiple options for each of):
* Display (LCD)
... and many more.
Interaction with the PMU/PMIC is required for at least some of the boot
Interaction with the display (LCD) while not technically required to
simply boot the kernel is required by desired use-cases, in order to
display a splash screen ASAP during early boot.
Oh, and the motherboard has a gazillion different HW mux options, which
affect, amongst many other things, which SD/eMMC/SDIO ports are usable
on the motherboard, and which are routed to various daughter boards. I'm
not actually 100% sure if the switches controlling those mux settings
are readable from SW. I certainly hope so...
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