Re: [Qemu-devel] [PATCH for-1.6] target-mips: do not raise exceptions when accessing invalid memory

[Aurélien Jarno]

On Mon, Aug 05, 2013 at 10:45:31AM +0200, Andreas Färber wrote:
> Am 05.08.2013 00:04, schrieb Aurélien Jarno:
> > On Mon, Jul 29, 2013 at 10:35:31PM +0200, Stefan Weil wrote:
> >> Am 27.07.2013 22:58, schrieb Stefan Weil:
> >>> Am 27.07.2013 22:43, schrieb Andreas Färber:
> >>>> Am 27.07.2013 21:37, schrieb Stefan Weil:
> >>>>> Am 27.07.2013 19:43, schrieb Peter Maydell:
> >>>>>> On 27 July 2013 17:18, Hervé Poussineau <address@hidden> wrote:
> >>>>>>> Another solution would be to add a big dummy memory regions on all 
> >>>>>>> MIPS boards
> >>>>>>> to catch memory accesses and not raise an exception. However, this 
> >>>>>>> means that
> >>>>>>> each MIPS board will have its own unassigned memory handler, 
> >>>>>>> different from the
> >>>>>>> global QEMU one.
> >>>>>> Better would be to at least provide fake RAZ/WI implementations of
> >>>>>> devices for the boards, rather than making the dummy region cover
> >>>>>> the whole of the address space. Not 1.6 material, though.
> >>
> >>
> >> For MIPS Malta, Linux boot can be fixed by handling read access for two
> >> addresses:
> >>
> >> 0x1fbf8008
> >> 0x1bc80110
> >>
> >> The corresponding definitions in the Linux kernel code seem to be these
> >> lines:
> >>
> >> #define GCMP_BASE_ADDR                  0x1fbf8000
> >> #define GCMP_ADDRSPACE_SZ               (256 * 1024)
> >> #define GCMP_GCB_GCMPB_OFS              0x0008          /* Global GCMP
> >> Base */
> >>
> >> #define MSC01_BIU_REG_BASE              0x1bc80000
> >> #define MSC01_BIU_ADDRSPACE_SZ          (256 * 1024)
> >> #define MSC01_SC_CFG_OFS                0x0110
> >>
> >> => mips_malta.c needs a handler for reads of
> >> (GCMP_BASE_ADDR + GCMP_GCB_GCMPB_OFS) and
> >> (MSC01_BIU_REG_BASE + MSC01_SC_CFG_OFS).
> > 
> > I don't think it would be correct to emulate them as this are not
> > present on the real Malta board, at least for the model emulated by
> > QEMU. Theses addresses correspond to the SMP controller, and is
> > therefore only present when an SMP daughter card is installed.
> > 
> > The Linux kernel probes theses addresses, and look if they return
> > something consistent. If not the corresponding devices are latter
> > ignored.
> > 
> > The real hardware probably returns all 1 or all 0 for addresses not
> > decoded to a device. This is what QEMU should model, and it should
> > not trigger a DBE or IBE exception.
> [snip]
> 
> Have you tested Jan's patches limiting the new unassigned read value -1
> to PIO?
> 

I have tried this patches, and they don't fix the problem.


-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net