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Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter |
Date: |
Thu, 17 Jun 2010 10:30:15 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Gleb Natapov wrote:
> On Thu, Jun 17, 2010 at 09:17:51AM +0200, Jan Kiszka wrote:
>> 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 <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? ;)
>>>> 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.
>>
> Sorry, I lost you here. What "works for IO-based fw-cfg, but not for
> MMIO-based".
Undefined IO ports return -1, undefined (/wrt read access) MMIO 0. So
you need to select a key that is different from both.
> Can you write pseudo logic of how you think it
> all should work?
The firmware should do this:
write(CTL_BASE, FW_CFG_ID);
if (read(CTL_BASE) != FW_CFG_ID)
deal_with_old_qemu();
else
check_for_supported_keys();
Jan
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- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, (continued)
- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/16
- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/16
- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/16
- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/16
- [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter,
Jan Kiszka <=
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Jan Kiszka, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter, Gleb Natapov, 2010/06/17