From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36928) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zotbs-0001x6-QU for qemu-devel@nongnu.org; Wed, 21 Oct 2015 09:39:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zotbp-0005l7-MG for qemu-devel@nongnu.org; Wed, 21 Oct 2015 09:39:20 -0400 Received: from mga01.intel.com ([192.55.52.88]:39239) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zotbo-0005iI-S7 for qemu-devel@nongnu.org; Wed, 21 Oct 2015 09:39:17 -0400 References: <1445216059-88521-1-git-send-email-guangrong.xiao@linux.intel.com> <1445216059-88521-29-git-send-email-guangrong.xiao@linux.intel.com> <20151020155149.GB2772@stefanha-thinkpad.home> <56266B3B.4080407@linux.intel.com> <20151021104937.GD13408@stefanha-thinkpad.redhat.com> From: Xiao Guangrong Message-ID: <562793F6.5090904@linux.intel.com> Date: Wed, 21 Oct 2015 21:32:38 +0800 MIME-Version: 1.0 In-Reply-To: <20151021104937.GD13408@stefanha-thinkpad.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v4 28/33] nvdimm acpi: support DSM_FUN_IMPLEMENTED function List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: ehabkost@redhat.com, kvm@vger.kernel.org, mst@redhat.com, gleb@kernel.org, Stefan Hajnoczi , mtosatti@redhat.com, qemu-devel@nongnu.org, pbonzini@redhat.com, imammedo@redhat.com, dan.j.williams@intel.com, rth@twiddle.net On 10/21/2015 06:49 PM, Stefan Hajnoczi wrote: > On Wed, Oct 21, 2015 at 12:26:35AM +0800, Xiao Guangrong wrote: >> >> >> On 10/20/2015 11:51 PM, Stefan Hajnoczi wrote: >>> On Mon, Oct 19, 2015 at 08:54:14AM +0800, Xiao Guangrong wrote: >>>> +exit: >>>> + /* Write our output result to dsm memory. */ >>>> + ((dsm_out *)dsm_ram_addr)->len = out->len; >>> >>> Missing byteswap? >>> >>> I thought you were going to remove this field because it wasn't needed >>> by the guest. >>> >> >> The @len is the size of _DSM result buffer, for example, for the function of >> DSM_FUN_IMPLEMENTED the result buffer is 8 bytes, and for >> DSM_DEV_FUN_NAMESPACE_LABEL_SIZE the buffer size is 4 bytes. It tells ASL code >> how much size of memory we need to return to the _DSM caller. >> >> In _DSM code, it's handled like this: >> >> "RLEN" is @len, “OBUF” is the left memory in DSM page. >> >> /* get @len*/ >> aml_append(method, aml_store(aml_name("RLEN"), aml_local(6))); >> /* @len << 3 to get bits. */ >> aml_append(method, aml_store(aml_shiftleft(aml_local(6), >> aml_int(3)), aml_local(6))); >> >> /* get @len << 3 bits from OBUF, and return it to the caller. */ >> aml_append(method, aml_create_field(aml_name("ODAT"), aml_int(0), >> aml_local(6) , "OBUF")); >> >> Since @len is our internally used, it's not return to guest, so i did not do >> byteswap here. > > I am not familiar with the ACPI details, but I think this emits bytecode > that will be run by the guest's ACPI interpreter? > > You still need to define the endianness of fields since QEMU and the > guest could have different endianness. > > In other words, will the following work if a big-endian ppc host is > running a little-endian x86 guest? > > ((dsm_out *)dsm_ram_addr)->len = out->len; > Er... If we do byteswap in QEMU then it is also needed in ASL code, however, ASL lacks this kind of instruction. I guess ACPI interpreter is smart enough to change value to Littel-Endian for all 2 bytes / 4 bytes / 8 bytes accesses I will do the change in next version, thanks for you pointing it out, Stefan!