From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40xZZq2FctzDrbk for ; Fri, 1 Jun 2018 03:44:03 +1000 (AEST) Date: Thu, 31 May 2018 20:43:58 +0300 From: "Michael S. Tsirkin" To: Anshuman Khandual Cc: Ram Pai , robh@kernel.org, aik@ozlabs.ru, jasowang@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hch@infradead.org, joe@perches.com, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, david@gibson.dropbear.id.au Subject: Re: [RFC V2] virtio: Add platform specific DMA API translation for virito devices Message-ID: <20180531204320-mutt-send-email-mst@kernel.org> References: <20180522063317.20956-1-khandual@linux.vnet.ibm.com> <20180523213703-mutt-send-email-mst@kernel.org> <20180524072104.GD6139@ram.oc3035372033.ibm.com> <0c508eb2-08df-3f76-c260-90cf7137af80@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <0c508eb2-08df-3f76-c260-90cf7137af80@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, May 31, 2018 at 09:09:24AM +0530, Anshuman Khandual wrote: > On 05/24/2018 12:51 PM, Ram Pai wrote: > > On Wed, May 23, 2018 at 09:50:02PM +0300, Michael S. Tsirkin wrote: > >> subj: s/virito/virtio/ > >> > > ..snip.. > >>> machine_subsys_initcall_sync(pseries, tce_iommu_bus_notifier_init); > >>> + > >>> +bool platform_forces_virtio_dma(struct virtio_device *vdev) > >>> +{ > >>> + /* > >>> + * On protected guest platforms, force virtio core to use DMA > >>> + * MAP API for all virtio devices. But there can also be some > >>> + * exceptions for individual devices like virtio balloon. > >>> + */ > >>> + return (of_find_compatible_node(NULL, NULL, "ibm,ultravisor") != NULL); > >>> +} > >> > >> Isn't this kind of slow? vring_use_dma_api is on > >> data path and supposed to be very fast. > > > > Yes it is slow and not ideal. This won't be the final code. The final > > code will cache the information in some global variable and used > > in this function. > > Right this will be a simple check based on a global variable. > Pls work on a long term solution. Short term needs can be served by enabling the iommu platform in qemu. -- MST