[coreboot] bug YT as EHCI gadget for coreboot

[John Lewis]

On 07/09/14 09:21, Denis 'GNUtoo' Carikli wrote:
> On Fri, 05 Sep 2014 09:14:12 +0100
> John Lewis <jlewis at johnlewis.ie> wrote:
>
>> On 05/09/14 07:17, Denis 'GNUtoo' Carikli wrote:
>>
>>> 4. Use your rasberry and try to make g_dbgp work there, to test use
>>> the linux kernel with earlyprintk=dbgp. Note that earlyprintk=dbgp
>>> doesn't work out of the box on all distro's kernels, you need the
>>> right compilation options to make it work.
>>>
>>> Denis.
>>
>> That won't work, I think, as the Pi uses the same micro-USB port
>> you'd be using for debug, for power.
> Why is that a problem, you could:
> * Get an usb cable with two "host" connectors: one on for the target
>    laptop, another one for the 5v power, and the usual one for the
>    rasberry side.
>    Such cables were common for mini-usb, for instance for hard disks
>    that didn't have enough power with only one usb port.
>    So you could get one, or make one, or make someone do it for you.
> * You may even not need such cable when testing g_dbgp and the
>    kernel's earlyprintk.
>
> Denis.

I'm not saying that wouldn't work, but splitters sometimes introduce 
problems, experience has taught me. I wouldn't be recommending it to 
someone as a solution that will work without issue. I think the second 
USB connector would possibly want to be wired so that it just carries power.

Yep, I fully accept that you could just leave the device at the Grub 
menu while you fire up the Pi for testing purposes, but ultimately we're 
talking about debugging firmware.

It's moot anyway as it was pointed out that the Pi doesn't have the 
necessary features in it's port.

John.