Re: [Qemu-arm] [PATCH] bcm2835_property: use cached values when querying framebuffer

[Stephen Warren <swarren@wwwdotorg.org>]

On 04/21/2016 08:07 AM, Sylvain Garrigues wrote:
> Le 21 avr. 2016 à 15:42, Peter Maydell <peter.maydell@linaro.org> a écrit :
>>
>> There may be something we can do here to make FreeBSD's life
>> easier, but we definitely can't do it on the eve of a release.
>
> I didn’t know it was release day, my timing is not perfect then, sorry about that, I didn’t intend to put stress on you guys today.
> Like you mentioned, the Linux boot protocol doesn’t mandate any loading address, hence the possibility to set it on the command line.
> It would benefit not only to FreeBSD (which is strictly Linux boot ABI compliant BTW - that is how I found the qemu bootloader bug and fixed it in b4850e5) but all other OS.
> On the real hardware Raspberry Pi, there is the kernel_address firmware feature which enable to set the kernel load address. Would be neat to have it *someday* in qemu for any board if it is not too hard to implement.

It would indeed be nice if qemu for the Pi implemented the exact same 
bootloader setup as real HW does. That is, loading boot images from the 
FAT partition on the SD card, parsing config.txt, etc.

Ideally as was mentioned earlier this would be done by simply executing 
the existing bootloader under emulation, rather than building all that 
code into qemu. However, in the Pi case, the bootloader runs on the 
VideoCore (a separate non-ARM CPU), so isn't (and likely won't be since 
IIUC it isn't fully documented) emulated by qemu. by the time the ARM 
CPU runs, everything (kernel, DTB/ATAGS, ARM boot stub, ...) is already 
loaded into RAM, the display is already probed over HDMI and the 
controller scanning out a dummy image, etc.

So I think if that were to be supported, it'd have to be coded into 
qemu. Is that something that could happen, or would such patches not fit 
qemu's model well?