BCM2836 (Raspberry Pi 2) port

Stephen Warren swarren at wwwdotorg.org
Fri Apr 24 11:57:05 PDT 2015

On 04/24/2015 12:41 PM, Eric Anholt wrote:
> Stephen Warren <swarren at wwwdotorg.org> writes:
>> On 04/21/2015 12:09 PM, Eric Anholt wrote:
>>> This is my first submission of a Raspberry Pi 2 port.  It can be found
>>> at https://github.com/anholt/linux/tree/bcm2836
>>> I'm using the 2835 interrupt controller support, without adding the
>>> checks for ARM local interrupts first.  That means no support for IPIs
>>> (and thus no SMP), no PMU events, and no local timer (I'm using the
>>> same 2835 peripheral one).
>>> It supports a similar featureset to Pi 1 at this point.  Serial and SD
>>> cards work.  Just one CPU supported.  USB (ethernet) works if you use
>>> U-Boot, or my mailbox series
>>> (https://github.com/anholt/linux/tree/bcm2836-mbox).
>> I can't quite get this to work. I think what's happening is that U-Boot
>> is over-writing the location of the code/data that the CPU1..3 pin loop
>> uses. Do you know what that address is so I can confirm that?
>> I suspect this because when I load the kernel/DT in U-Boot, or when I
>> jump to the kernel to boot it, I see lots of extra duplicated characters
>> on the UART, like all 4 CPUs are booting Linux. For example:
> Oops, I was just extrapolating that U-Boot would work.  I've quit using
> it because of the extra configuration work (particularly the compiled
> text files for the boot scripts).

You don't need any compiled text files if you create an extlinux.conf 
rather than a boot.scr. extlinux.conf is plain text.

To boot without U-Boot: Could you say what's in your config.txt? I 
assume I can just copy the kernel zImage as kernel.img, and the DTB from 
the kernel build tree without renaming it?

> I haven't looked into how SMP works, because I don't have the interrupt
> support necessary yet (bcm2836-irq branch for hacks in that direction).
> And in further testing, the USB is actually not working and I'm not sure
> what gave me the idea that it was.

It might be intermittent depending on (GPU) cache content. We need to 
fix the kernel in a similar fashion to the following U-Boot commits:

> http://git.denx.de/?p=u-boot.git;a=commit;h=79340db7f1f676b8eb5911f4993ebedf27009c0b
ARM: bcm2835: implement phys_to_bus/bus_to_phys

> http://git.denx.de/?p=u-boot.git;a=commit;h=5c0beb5c58c86d2a6d12dee6330dc85554de5c60
usb: dwc2: use phys_to_bus/bus_to_phys

> http://git.denx.de/?p=u-boot.git;a=commit;h=122426d46e31391480c4b83b1003e4feca24d491
ARM: bcm2835: use phys_to_bus() for mbox

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