[RFC] mailbox: Add Broadcom BCM2835 mailbox driver

[Craig McGeachie]

On 08/22/2013 05:07 AM, Stephen Warren wrote:
> Using a different SD card might make a difference. Different cards
> support different transfer modes, and it's quite possible the upstream
> driver is advertising support for some modes that need additional HW bug
> workarounds that aren't present.
>
> Also, which U-Boot are you using? The one with USB support is based on a
> rather old U-Boot code-base; perhaps try Denx's official u-boot.git?

I was using the one from https://github.com/gonzoua/u-boot-pi.  I had 
thought about revisiting Denx's official one. When I looked at that and 
found out that if I had issues the only supported debugging technique 
was JTAG, I decided I'd better break out the debugger I'd bought, but 
had not been brave enough to try out.  Turned out to be easier that I 
thought.

Of course once I did that, I realised I now had a fairly good solution 
for bootstrapping the kernel.  I'm using armjtag.bin by David Welch as a 
bootloader.  Halt the CPU, fdtput on the bcm2835-rpi-b.dtb file (set the 
kernel command line), load up the binaries to the right locations, set 
the registers as per booting ARM specification, and resume the CPU from 
the kernel entry point.

Probably a very round about way of doing it, but it suits me just fine. 
  I can be confident about exactly how the kernel is being booted.  I 
can manually tailor the device tree any way I like without fear of 
interference.  It's a bit more manual, and the kernel takes about 100 
seconds to transfer, but personally I like the aspect of knowing what is 
going on.

But thank you for the advice about the SD card and trying another U-Boot 
code base.  I may well revisit that if I get time.  Having a properly 
working U-Boot for the Raspberry Pi seems like a seriously good thing.

Cheers,
Craig.