From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35238) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uyt8J-0007mR-7K for qemu-devel@nongnu.org; Mon, 15 Jul 2013 20:28:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Uyt8F-0001C6-Vx for qemu-devel@nongnu.org; Mon, 15 Jul 2013 20:28:47 -0400 Received: from mail-ie0-f178.google.com ([209.85.223.178]:45412) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uyt8F-0001Br-QO for qemu-devel@nongnu.org; Mon, 15 Jul 2013 20:28:43 -0400 Received: by mail-ie0-f178.google.com with SMTP id u16so194049iet.9 for ; Mon, 15 Jul 2013 17:28:43 -0700 (PDT) From: Anthony Liguori In-Reply-To: <51E48086.1040307@ozlabs.ru> References: <1373614639-15523-1-git-send-email-aik@ozlabs.ru> <20130713080309.GA11522@voom.redhat.com> <51E2A614.5010402@ozlabs.ru> <87vc4bamst.fsf@codemonkey.ws> <51E48086.1040307@ozlabs.ru> Date: Mon, 15 Jul 2013 19:28:40 -0500 Message-ID: <871u6ztkjr.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [Qemu-devel] [PATCH] spapr-pci: change endianness for io ports space List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy Cc: Alexander Graf , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, David Gibson Alexey Kardashevskiy writes: > On 07/16/2013 01:02 AM, Anthony Liguori wrote: >> Alexey Kardashevskiy writes: >> >>> On 07/13/2013 06:03 PM, David Gibson wrote: >>>> On Fri, Jul 12, 2013 at 05:37:19PM +1000, Alexey Kardashevskiy wrote: >>>>> sPAPR PHB emulates IO ports on PCI via a special memory region which >>>>> routes all reads/writes further via cpu_in*/cpu_out* which are eventually >>>>> processed by MemoryRegionOps implemented by devices. >>> >>>> Hrm. That double dispatch was a workaround for bugs in the plain >>>> memory region dispatching which meant we couldn't directly map regions >>>> in memory space to IO areas. >>>> >>>> It would be worth checking if that workaround is still necessary. >>> >>> Hm. Good point, thanks! It seems memory_region_init_io is not necessary any >>> more. Will make a patch for it. >> >> You should try the latest qemu.git commit. There shouldn't be a problem >> anymore. > > > Does this mean sPAPR still needs an additional IO memory region? It looks > redundand and everything (almost) works without it... There's more brokenness... Some ISA devices mark themselves as "little endian" whereas others mark themselves as "native endian". "little endian" really means "do byte lane swapping during dispatch" if host endian != target endian. So on sPAPR, what you're getting is the redundant IO memory region causing a byte lane swap which is then negated by the ISA devices that mark themselves as little endian (such as VGA). The right solution is to drop the additional IO region on sPAPR and remove the ISA devices marking themselves as "little endian". But that requires careful testing and fixing the other platforms that also are relying on the doube byte lane swapping. Regards, Anthony Liguori > > > -- > Alexey