[Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jun 16, 2010 at 11:33:13AM +0200, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > On Wed, Jun 16, 2010 at 09:57:35AM +0200, Jan Kiszka wrote:
> >> Gleb Natapov wrote:
> >>> On Wed, Jun 16, 2010 at 09:51:14AM +0200, Jan Kiszka wrote:
> >>>> Gleb Natapov wrote:
> >>>>> On Wed, Jun 16, 2010 at 09:03:01AM +0200, Jan Kiszka wrote:
> >>>>>> Gleb Natapov wrote:
> >>>>>>> On Wed, Jun 16, 2010 at 12:40:28AM +0200, Jan Kiszka wrote:
> >>>>>>>> From: Jan Kiszka <jan.kiszka@siemens.com>
> >>>>>>>>
> >>>>>>>> There is no need starting with the special value for hpet_cfg.count.
> >>>>>>>> Either Seabios is aware of the new firmware interface and properly
> >>>>>>>> interprets the counter or it simply ignores it anyway.
> >>>>>>>>
> >>>>>>> I want seabios to be able to distinguish between old qemu and new one.
> >>>>>> I see now. But isn't it a good chance to introduce a proper generic
> >>>>>> interface for exploring supported fw-cfg keys?
> >>>>>>
> >>>>> Having such interface would be nice. Pity we haven't introduced it from
> >>>>> the start. If we do it now seabios will have to find out somehow that
> >>>>> qemu support such interface. Chicken and egg ;)
> >>>> That is easy: Add a key the describes the highest supported key value
> >>>> (looks like this is monotonously increasing). Older qemu versions will
> >>>> return 0.
> >>>>
> >>> That will not support holes in key space, and our key space is already
> >>> sparse.
> >> Then add a service to obtain a bitmap of supported keys. If that bitmap
> >> is empty...
> >>
> > Bitmap will be 2k long. We can add read capability to control port. To
> > check if key is present you select it (write its value to control port)
> > and then read control port back. If values is non-zero the key is valid.
> > But how to detect qemu that does not support that?
> 
> Isn't there some key that was always there and will always be?
> 
FW_CFG_SIGNATURE

--
			Gleb.