On Thu, Jan 30, 2014 at 12:45 PM, Jason Cooper jason@lakedaemon.net wrote:
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. :)
our eeprom config section is only 40 bytes. It contains a SKU string, mac addrs, and some bitwise fields for the various optional components that we can subload.
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?
yes its a valid dtb - it is just the superset of everything the baseboard (ie schematic design) can support.
A good example is a custom SKU of a baseboard with ethernet subloaded. If the EEPROM says there is no ethernet mac or phy, I would want to remove or disable the ethernet node from the devicetree.
Another example would be a node for 'gpio-pps' (GPIO based pulse-per-second) support. A baseboard design that has a GPS with its PPS signal tied to a GPIO would define this in the device-tree, but if the EEPROM says the GPS isn't loaded, I would want to remove or disable the gps-pps node.
Tim
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.