From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=48559 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OP9MM-0002US-FQ for qemu-devel@nongnu.org; Thu, 17 Jun 2010 03:17:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OP9ML-0003p8-8Y for qemu-devel@nongnu.org; Thu, 17 Jun 2010 03:17:58 -0400 Received: from fmmailgate02.web.de ([217.72.192.227]:43688) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OP9MK-0003ov-Ra for qemu-devel@nongnu.org; Thu, 17 Jun 2010 03:17:57 -0400 Message-ID: <4C19CC1F.9040209@web.de> Date: Thu, 17 Jun 2010 09:17:51 +0200 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter 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> <20100617054857.GH523@redhat.com> In-Reply-To: <20100617054857.GH523@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigB157F0B05BA04210FB1C2FFD" Sender: jan.kiszka@web.de List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: qemu-devel This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigB157F0B05BA04210FB1C2FFD Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 >>>>>>>>>>>>> >>>>>>>>>>>>> There is no need starting with the special value for hpet_c= fg.count. >>>>>>>>>>>>> Either Seabios is aware of the new firmware interface and p= roperly >>>>>>>>>>>>> interprets the counter or it simply ignores it anyway. >>>>>>>>>>>>> >>>>>>>>>>>> I want seabios to be able to distinguish between old qemu an= d new one. >>>>>>>>>>> I see now. But isn't it a good chance to introduce a proper g= eneric >>>>>>>>>>> interface for exploring supported fw-cfg keys? >>>>>>>>>>> >>>>>>>>>> Having such interface would be nice. Pity we haven't introduce= d it from >>>>>>>>>> the start. If we do it now seabios will have to find out someh= ow 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 versio= ns will >>>>>>>>> return 0. >>>>>>>>> >>>>>>>> That will not support holes in key space, and our key space is a= lready >>>>>>>> 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= =2E 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 suppor= t >> 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 --------------enigB157F0B05BA04210FB1C2FFD Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkwZzCIACgkQitSsb3rl5xRVugCdE1wiswnTaFuDBfHwW4R6x8tO 6/8AoMg1UjRuVkV4xlPgbL9Y7Bs2v4kt =h/dB -----END PGP SIGNATURE----- --------------enigB157F0B05BA04210FB1C2FFD--