Re: [Qemu-devel] Is realview-pb-a8 fully supported ?

[Alexander Graf]

On 09.10.2011, at 14:51, Peter Maydell wrote:

> On 9 October 2011 13:06, Francis Moreau <address@hidden> wrote:
>> On Sun, Oct 9, 2011 at 12:48 PM, Peter Maydell <address@hidden> wrote:
>>> On 9 October 2011 09:28, Francis Moreau <address@hidden> wrote:
>>>> I'm trying to use qemu to emulate the ARM realview-pb-a8 and more
>>>> specifically I'd like to boot using the SD interface.
>>>> 
>>>> However it looks like some devices are not emulated at all on this
>>>> platform.
>>> 
>>> Correct; not all devices are emulated.
> 
>> May I suggest to report that a platform is partially supported when
>> doing "qemu -M ?"
> 
> I suspect that (in the sense you seem to be using "partially supported")
> would cover almost all the platforms QEMU supports. Device and board
> modelling is not trivial, and the typical state is that devices may be
> missing, or have unimplemented features, or have bugs.
> 
> The platform is supported in the sense that if you report regressions
> (ie things that used to work and have broken) I will look at them, and
> if you submit patches to improve it I will review them.
> 
>> However, those are still missing:
>> 
>> amba_device_register failed to register dev:smc
>> amba_device_register failed to register dev:sctl
>> amba_device_register failed to register dev:wdog
>> amba_device_register failed to register dev:sci0
>> amba_device_register failed to register dev:ssp0
>> amba_device_register failed to register fpga:aaci
> 
> Do you actually *need* these devices? If so, you're
> going to need to model them. (except "fpga:aaci", which
> is the PL041 audio; there are patches going through review
> for that currently.) But in general Linux will quite happily
> boot even if some of the minor devices are missing.
> 
>> In your opinion, which plateform should I use to get a fully supported
>> platform based on ARMv7 cpu ?
> 
> I would recommend vexpress-a9 over realview-pb-a8 simply because
> it's newer; nobody cares much about pb-a8 hardware any more.
> The actual level of support (in terms of which devices are
> present and how fully featured they are) is about the same, though.
> 
>>> NB: when booting off SD card make sure you use
>>> "-drive if=sd,cache=writeback,file=your-sd.img", otherwise you
>>> will get the writethrough cache and really poor I/O performance.
>>> [the slight catch is that if your *host* system crashes you
>>> may get disk corruption, but typically for ARM emulation use
>>> cases that is acceptable.]
>> 
>> Thanks for the tip but why not making writeback the defaut ?
> 
> Because of the 'slight catch' I mentioned.

cache=writeback survives host crashes. The only reason writethrough is the 
default is Windows XP which doesn't issue flushes properly, so there 
cache=writeback can lead to data loss. Linux guests are fine.


Alex