From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=58056 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OP7yI-0003Gh-3l for qemu-devel@nongnu.org; Thu, 17 Jun 2010 01:49:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OP7yG-0006YB-PS for qemu-devel@nongnu.org; Thu, 17 Jun 2010 01:49:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61855) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OP7yG-0006Y4-I1 for qemu-devel@nongnu.org; Thu, 17 Jun 2010 01:49:00 -0400 Date: Thu, 17 Jun 2010 08:48:57 +0300 From: Gleb Natapov Subject: Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter Message-ID: <20100617054857.GH523@redhat.com> References: <4C187725.2000902@web.de> <20100616073318.GZ21797@redhat.com> <4C188272.9010201@web.de> <20100616075259.GA21797@redhat.com> <4C1883EF.10109@web.de> <20100616090658.GC21797@redhat.com> <4C189A59.3040300@web.de> <20100616093516.GD21797@redhat.com> <20100616153607.GG523@redhat.com> <4C18F538.1090709@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C18F538.1090709@web.de> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: qemu-devel 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 > >>>>>>>>>>> > >>>>>>>>>>> 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. -- Gleb.