Re: [Qemu-devel] Update the id of Vexpress Cortex-A9 from r0p0 to r0p1?

[Peter Maydell]

On 6 October 2013 20:12, Mian Yousaf Kaukab <address@hidden> wrote:
> Default vexpress_defconfig does not boot on qemu vexpress-a9 target. In 
> kernel,
> vexpress uart detection for DEBUG_LL is done using Coretex-A9 id. Only r0p1 is
> mapped to legacy map. All other variants are mapped to RS1/aseries map.

Detecting the board model based on the CPU revision-and-patchlevel is a
horrible hack and I wish the kernel guys would drop it.

Really the kernel should provide a way to specify (in the device tree
or otherwise)
where the UART is, in a way that the early kernel code can easily get at to use
for its earlyprint uart.

> As qemu vexpress-a9 target reports Cortex-A9 version as r0p0, kernel maps 
> uart0
> at address 0x1c090000 instead of 0x10009000. This result in kernel 
> indefinitely
> waiting for uart during boot. A kernel patch to fix this was discussed
> in the following link
> http://comments.gmane.org/gmane.linux.ports.arm.kernel/269657 .
> In this discussion Pawel Moll mentioned that V2P-CA9 has Cortex-A9 r0p1 and 
> not
> r0p0. If this is correct, to fix this and similar future problems, shouldn't
> qemu Cortex-A9 be updated to version r0p1?

The trouble is that QEMU models CPUs and boards separately and
doesn't model every single variant/patchlevel of each CPU, because
that would be a fairly large amount of extra effort.

> So what will it take to update the id of Cortex-A9 in qemu from r0p0 to r0p1?

If we're updating, why would we update only to r0p1 and not to the most
recent rev/patchlevel?

The major thing we need is a mechanism for allowing at least the
board, and possibly also the user, to specify properties of the cpu
like "which rev/patchlevel is it" (being able to specify "do we have an
fpu/neon/etc" is a similar thing).

If we had that it would not be too hard to then have the vexpress-a9
board specify which rev/patchlevel to use. But we don't have the
mechanism currently.

-- PMM