[U-Boot] [PATCH 00/20] arm: rpi: Enable USB and Ethernet driver model Raspberry Pi

[Stephen Warren]

On 07/14/2015 09:44 AM, Simon Glass wrote:
> Hi Stephen,
> 
> On 13 July 2015 at 22:52, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 07/11/2015 08:04 AM, Simon Glass wrote:
>>> Hi Stephen,
>>>
>>> On 10 July 2015 at 23:34, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>>> On 07/07/2015 08:53 PM, Simon Glass wrote:
>>>>> Raspberry Pi uses a DWC2 USB controller and a SMSC USB Ethernet adaptor.
>>>>> Neither of these currently support driver model.
>>>>>
>>>>> This series does the following:
>>>>> - Move Raspberry Pi to use device tree control (u-boot-dtb.bin instead of
>>>>>      u-boot.bin)
>>>>
>>>> I'd strongly prefer not to do this. For one thing, it means we'd need
>>>> different U-Boot builds for each of the different RPi models, and we
>>>> currently don't need that (or perhaps we require users to create their
>>>> own u-boot-dtb.bin by choosing the right DTB to append). If it
>>>
>>> Why does device tree change how things work now? The get_board_rev()
>>> function currently deals with this. It doesn't look like rpi_board_rev
>>> is used anywhere else.
>>
>> Without a DT, the code is free to make all the board-rev-specific
>> decisions at run-time without external influence.
>>
>> With a DT, we either have to:
>>
>> a) Pick the DT for one particular board and use that everywhere, even if
>> it's incorrect for the actual board in use.
>>
>> b) Build a different U-Boot + DTB image for each board-rev, and put the
>> correct one on the SD card.
>>
>> Neither of those options seem like a good idea to me.
> 
> How about:
> 
> c) Leave the code as is, and not add a whole lot more device tree files.
> 
> After all the kernel only has files for rpi and rpi_2. Why should we
> add one for each variant? If you don't want to do it, why do it?

For the kernel I do expect to add a DT file for each variant. That makes
sense since we expect a single kernel binary to run unmodified on all
HW, parameterize the HW setup via the DTB, and have an infrastructure to
pass the different DTs to the kernel easily.

For U-Boot, I'd like to continue to have a single-binary that runs on
all RPis (well, one for RPi 1, another for RPi 2). That's a very nice
usage model for users. That's not possible if U-Boot pulls everything
from DT and we have a different DT for each system (which only makes
sense so that we don't lie in the DT, or fail to represent the
differences between the models) since a single DT is embedded into the
U-Boot binary; there's no infra-structure to passing 1 of n DTBs to U-Boot.