Gleb Natapov wrote: > On Wed, Jun 16, 2010 at 06:00:56PM +0200, Jan Kiszka wrote: >> Gleb Natapov wrote: >>> 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 <jan.kis...@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 >>>> >>> So any ideas? Or did I misunderstood your hint? ;) >> I thought you found the answer yourself: >> >> Seabios could select FW_CFG_SIGNATURE and then perform a read-back on >> the control register. Older QEMUs will return -1, versions that support >> the read-back 0. Problem solved, no? >> > AFAIK QEMU returns 0 if io read was done from non-used port or mmio > address, but can we rely on this? If we can then problem solved, if > we can't then no.
It works for IO-based fw-cfg, but not for MMIO-based. So the firmware should probably pick a non-zero key for this check, e.g. FW_CFG_ID. Jan
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