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

[Gleb Natapov]

On Wed, Jun 16, 2010 at 12:35:16PM +0300, Gleb Natapov wrote:
> 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 <address@hidden>
> > >>>>>>>>
> > >>>>>>>> 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
> 
So any ideas? Or did I misunderstood your hint? ;)

--
                        Gleb.