recommended action for bootloaders regarding modifying device-tree nodes

[Jason Cooper]

Hi Tim,

On Thu, Jan 30, 2014 at 01:11:18AM -0800, Tim Harvey wrote:
> My approach has been to define a per-baseboard device-tree in Linux
> for a 'fully loaded' board, then remove nodes which the EEPROM claims
> are not present in the bootloader before it passes the DTB to the
> kernel.  I do this by defining aliases in the device-tree for the
> peripherals that are 'optional' so that the bootloader itself does not
> need to know the details about how the device is connected.

This is more of a process question:  Is there any information captured
in your EEPROM that can't be represented in the dtb?  iow, at the point
when you write the EEPROM, why not write the dtb to it as configured?

You could have pre-configured dtsi fragments for each config option, and
then dynamically create the board dts from the order.

I only ask because it would solve the problem below.  However, there's a
lot more to changing a manufacturing process than meets the eye. :)

> Is it more appropriate for the bootloader to 'remove' nodes for
> devices that are not physically present or should I be setting their
> status property to 'disabled' instead?  I'm not clear if either option
> really has any pros or cons.

That depends on how you have it structured.  Is it a valid dtb?
Meaning, do you have four nodes all at the same register address?
Perhaps you could provide an example dts?

thx,

Jason.

> Tim Harvey - Principal Software Engineer
> Gateworks Corporation

btw - one of my first embedded projects was on one of your boards. An
ixp425 with 4 mini-pci slots.