[meta-xilinx] Linux/FreeRTOS AMP vrings

[Edward Wingate]

On Tue, Sep 1, 2015 at 1:35 AM, Nathan Rossi <nathan at nathanrossi.com> wrote:
>
> So if you want the linux-xlnx_3.19 equivalent use commit id
> "3f30b3337af61f1ed98f7185e37c6bf9202b3204". And set the SRCREV in your
> local.conf like so:
>
> SRCREV_pn-linux-xlnx-dev = "3f30b3337af61f1ed98f7185e37c6bf9202b3204"
>

Thanks, Nathan, this worked perfectly.  I'm running kernel 3.19 now
and Linux is still giving vring buffer addresses of 0x1f440xxx to
CPU1, while reading from 0x1e440xxx.

To recap, Linux is putting rpmsg vring buffers at va 0x9f440000,
physical address 0x1e440000:
virtio_rpmsg_bus virtio0: buffers: va 9f440000, dma 0x1e440000

This is consistent with /proc/vmallocinfo:
0x9f000000-0xa1001000 33558528 dma_init_coherent_memory+0x4c/0xe0
phys=1e000000 ioremap

But then Linux is initializing the vring descriptors with buffer
addresses of 0x1f440xxx, instead of 0x1e440xxx.

When CPU1 writes data to the vring buffer and kicks Linux, Linux then
reads the buffer from 0x1e440xxx (which is consistent with where they
were allocated, but not consistent with what was told to CPU1).

Anyway, I'm at a total loss of where to go from here.  I want to get
to the bottom of this, but need to forge ahead and will just
manipulate the vring addresses on CPU1 side before reading/writing
them (and hope it doesn't come back to bite me too hard later).

Thanks all, for your help.  If you have any further ideas of where I
might look next, I'd appreciate hearing them.  I said before, I tried
to follow how the virtual-to-physical address conversion occurs, but I
got lost due to the many layers of macros that also depend on what CPU
architecture is in use.  But I wouldn't think there's such a glaring
bug in the virtual memory address conversion though.  There must be
something basic I'm missing or some misconfiguration on my part, but I
don't know what it could be.