RPi3 arm64 port status

[Eric Anholt]

Stephen Warren <swarren at wwwdotorg.org> writes:

> On 03/23/2016 07:52 PM, Eric Anholt wrote:
>> I spent today working on getting aarch64 working on the Raspberry Pi 3.
>> Here's what I've got so far:
>>
>> U-Boot branch mostly based on srwarren's work:
>> https://github.com/anholt/u-boot/tree/rpi_dev
>>
>> (Check the commit messages there for necessary config.txt contents)
>>
>> My linux tree:
>> https://github.com/anholt/linux/tree/bcm2837-64
>>
>> Linux is booting to the point of initializing MMC.  As of recently, I'm
>> seeing MMC hangs at boot, and I haven't tracked down what's changed.
>>
>> I haven't implemented SMP yet.  Just like the 2836, the firmware has the
>> secondaries spinlooping in a little bit of firmware memory, watching a
>> channel of the the inter-processor mailboxes.  When the secondary sees
>> the channel get a value, it jumps to it.  This is the same on the new
>> 64-bit chips, even though the register we're communicating through is
>> only 32 bits.
>
> Are you sure about that? I was under the impression that on the RPi 2, 
> the secondary CPU spin loop was implemented in a short stub that the VC 
> firmware placed into RAM at address 0 (the default ARM CPU reset 
> vector), but that that for the RPi 3 in AArch64 mode, there was no such 
> stub available yet.
>
> As such I made U-Boot link to address 0, relied on setting kernel_old=1 
> in config.txt (which causes U-Boot to be loaded at address 0) and 
> enabled a similar secondary CPU spin loop in U-Boot by enabling 
> CONFIG_ARMV8_MULTIENTRY=y. The U-Boot code waits for a write to a memory 
> location (currently hard-coded to a somewhat randomly chosen 0x0FFFFFF0) 
> rather than for a message to appear in the HW mailbox.

You're right.  I hadn't noticed anything change about it in the firmware
logs, so I was assuming the same mechanism, but I hadn't read up on what
kernel_old was doing.  I haven't had any luck with releasing from the
pen you've set up, yet, but I'm also way too tired at this point to
trust anything I'm doing.

(Also, a patch that gets MMC unstuck is now on the branch)
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