Re: [edk2-platforms: PATCH 1/1] Platform/RPi3: Accept "ethernet" or "ethernet0" aliases in device tree

[Michael Brown <mbrown@fensystems.co.uk>]

On 23/07/2019 11:34, Leif Lindholm wrote:
> On Fri, Jul 19, 2019 at 06:29:07PM +0100, Michael Brown wrote:
>> Older device trees tend to use the alias "ethernet".  Newer device
>> trees tend to use "ethernet0" since older versions of U-Boot would
>> skip aliases that do not include an index number.  See, for example,
>> Linux kernel commit 10b6c0c ("ARM: dts: bcm2835: add index to the
>> ethernet alias") and U-Boot commit f8e57c6 ("fdt_support: Fixup
>> 'ethernet' aliases not ending in digits").
>>
>> Accept either "ethernet" or "ethernet0" as being the alias to the node
>> for which the MAC address should be updated.
> 
> Why is this patch useful?
> I understand the problem, but we include the .dtb from our own
> edk2-non-osi tree. And it seems that device tree already provides an
> alias to support both:
> https://github.com/tianocore/edk2-non-osi/blob/master/Platform/RaspberryPi/RPi3/DeviceTree/bcm2710-rpi-3-b.dts
> 
> Would it be more useful to warn loudly if "ethernet" isn't present?
> (And just *replace* ethernet[0] with ethernet below.)

The device tree can also be provided by the VC4 firmware, e.g. with a 
config.txt containing e.g.

   device_tree_address=0x10000
   device_tree_end=0x20000
   device_tree=bcm2710-rpi-3-b-plus.dtb

It is also possible to omit the explicit "device_tree=..." and have just

   device_tree_address=0x10000
   device_tree_end=0x20000

This configuration will cause the VC4 firmware to automatically load the 
appropriate device tree file.  I have tested that this allows me to boot 
from a 3B or 3B+ using a single SD card image that contains all of the 
.dtb files from

   https://github.com/raspberrypi/firmware/tree/master/boot

These "official" raspberrypi-firmware .dtb files are built from the 
stock Linux kernel .dts files, and contain only "ethernet0".

To address your specific questions:

 > Why is this patch useful?

It allows us to boot using the "official" .dtb files without any 
unexpected behaviour.

This in turn allows us to boot with the VC4 firmware automatically 
selecting the appropriate .dtb file for the hardware.  This is extremely 
useful when trying to provide a single SD card image that will work on a 
wide range of hardware.

 > Would it be more useful to warn loudly if "ethernet" isn't present?
 > (And just *replace* ethernet[0] with ethernet below.)

This would also solve the problem.  I would find it mildly surprising 
behaviour if I were debugging around it, since the "official" .dtb files 
have moved in the other direction (going from "ethernet" to 
"ethernet0"), but I would not expect it to break anything.

Another option would be to have UpdateMacAddress() ensure that both 
"ethernet" and "ethernet0" aliases exist.

I am happy to work up a new version of the patch: just let me know which 
option you prefer.

Many thanks,

Michael