From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=51936 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OPAUX-0007YC-1v for qemu-devel@nongnu.org; Thu, 17 Jun 2010 04:30:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OPAUQ-0005Uv-OK for qemu-devel@nongnu.org; Thu, 17 Jun 2010 04:30:28 -0400 Received: from fmmailgate01.web.de ([217.72.192.221]:54731) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OPAUQ-0005UI-Cl for qemu-devel@nongnu.org; Thu, 17 Jun 2010 04:30:22 -0400 Message-ID: <4C19DD17.3000408@web.de> Date: Thu, 17 Jun 2010 10:30:15 +0200 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH] hpet: Clean up initial hpet counter References: <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> <4C19CC1F.9040209@web.de> <20100617080758.GK523@redhat.com> In-Reply-To: <20100617080758.GK523@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig2FC39A30EEFFFC86F242907D" 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) --------------enig2FC39A30EEFFFC86F242907D Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> 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 introdu= ced it from >>>>>>>>>>>> the start. If we do it now seabios will have to find out som= ehow that >>>>>>>>>>>> qemu support such interface. Chicken and egg ;) >>>>>>>>>>> That is easy: Add a key the describes the highest supported k= ey value >>>>>>>>>>> (looks like this is monotonously increasing). Older qemu vers= ions 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 tha= t bitmap >>>>>>>>> is empty... >>>>>>>>> >>>>>>>> Bitmap will be 2k long. We can add read capability to control po= rt. To >>>>>>>> check if key is present you select it (write its value to contro= l port) >>>>>>>> and then read control port back. If values is non-zero the key i= s 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 o= n >>>> the control register. Older QEMUs will return -1, versions that supp= ort >>>> 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) !=3D FW_CFG_ID) deal_with_old_qemu(); else check_for_supported_keys(); Jan --------------enig2FC39A30EEFFFC86F242907D 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 iEYEARECAAYFAkwZ3RsACgkQitSsb3rl5xTlsACeNBQ7aKVBfe0l8lhdnoaoucI6 wk4AoI49OZpZAqatKvVVBlfg7UXrS5pL =ki3g -----END PGP SIGNATURE----- --------------enig2FC39A30EEFFFC86F242907D--