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

[Jan Kiszka <jan.kiszka@web.de>]

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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?

Jan



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