Re: [Qemu-devel] [PATCH, RFC] pci: allow PCI devices to fix address space

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Jun 12, 2011 at 02:40:35PM +0200, Hervé Poussineau wrote:
> Andreas,
> 
> Andreas Färber a écrit :
> >
> >Hervé,
> >
> >Am 22.12.2010 um 07:49 schrieb Michael S. Tsirkin:
> >
> >>On Wed, Dec 22, 2010 at 07:30:33AM +0100, Hervé Poussineau wrote:
> >>>Isaku Yamahata a écrit :
> >>>>On Wed, Dec 22, 2010 at 12:20:23AM +0100, Andreas Färber wrote:
> >>>>>From: Hervé Poussineau <hpoussin@reactos.org>
> >>>>>
> >>>>>v1:
> >>>>>* Rebased.
> >>>>>
> >>>>>Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
> >>>>>Cc: Michael S. Tsirkin <mst@redhat.com>
> >>>>>Signed-off-by: Andreas Färber <andreas.faerber@web.de>
> >>>>>---
> >>>>>Hello Michael,
> >>>>>Could you please take a look at this? I'm out of my field here.
> >>>>>The intention of the first part appears to be to save (val & ~mask),
> >>>>>whereas the inline helper would've returned (val & mask).
> >>>>
> >>>>Such behavior is intended.
> >>>>The returned value is just discarded in this case.
> >>>>test-and-clear means
> >>>>    clear the bits
> >>>>    return if those cleared bits were really set.
> >>>>
> >>
> >>What about this first chunk? Is it necessary.
> >>
> >>>>>The second part makes existing code conditional on that value.
> >>>>
> >>>>What issue are you addressing?
> >>>>Although the spec doesn't says about the default value of
> >>>>BAR registers
> >>>>after reset, the current code assumes that almost all the
> >>>>pci devices clear
> >>>>those registers.
> >>>>Anyway after cold/warm reset firmware sets up BARs, so it
> >>>>doesn't matter.
> >>>>You, however, seem to want to keep BARs over resets.
> >>>>
> >>>>thanks,
> >>>>
> >>>>
> >>>As you have seen, the intend here is to be able to keep BARs
> >>>over resets.
> >>>It is required for some really specific devices, like a PCI to ISA
> >>>bridge, where MMIO is always at the same address.
> >>>In that case, the device keeps PCI_COMMAND_MEMORY and/or
> >>>PCI_COMMAND_IO flags as read-only.
> >>>
> >>>Hervé
> >>
> >>Aha. Are the BARs still writeable?  If not maybe that's the right thing
> >>to check? If yes maybe the device simply should have a reset
> >>handler to rewrite them?
> >
> >I haven't noticed a follow-up patch of yours.
> >
> >Since I don't know what to do here, I'll have to take this out of
> >the PReP queue for now.
> >Without this patch, I get to at least the second bootloader icon,
> >the PCI graphics still work. What particular symptoms did you
> >observe wrt the i82378 that we can reproduce?
> >
> >Thanks,
> >Andreas
> >
> 
> Try do do info qtree with and without this patch, and check the
> i82378 device
> With this patch, I have:
>        bar 0: mem at 0x80000000 [0x8000ffff]
>        bar 1: mem at 0xc0000000 [0xc0ffffff]
> 
> Without it, I have:
>        bar 0: mem at 0xffffffffffffffff [0xfffe]
>        bar 1: mem at 0xffffffffffffffff [0xfffffe]
> 
> I think that firmware doesn't initialize BARs for this device.

Interesting. So what set the BARs to these values (0x80000000
and 0xc0000000)?

> However, I don't know what can be the consequences of not doing it.
> 
> Regards,
> 
> Hervé