From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 415Jc82ZRSzF0Vt for ; Wed, 13 Jun 2018 17:42:00 +1000 (AEST) Date: Wed, 13 Jun 2018 00:41:41 -0700 From: Christoph Hellwig To: Benjamin Herrenschmidt Cc: Ram Pai , "Michael S. Tsirkin" , Christoph Hellwig , robh@kernel.org, pawel.moll@arm.com, Tom Lendacky , aik@ozlabs.ru, jasowang@redhat.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, joe@perches.com, "Rustad, Mark D" , david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, Anshuman Khandual Subject: Re: [RFC V2] virtio: Add platform specific DMA API translation for virito devices Message-ID: <20180613074141.GA12033@infradead.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> <20180531204320-mutt-send-email-mst@kernel.org> <20180607052306.GA1532@infradead.org> <20180607185234-mutt-send-email-mst@kernel.org> <20180611023909.GA5726@ram.oc3035372033.ibm.com> <07b804fccd7373c650be79ac9fa77ae7f2375ced.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <07b804fccd7373c650be79ac9fa77ae7f2375ced.camel@kernel.crashing.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Jun 11, 2018 at 01:29:18PM +1000, Benjamin Herrenschmidt wrote: > At the risk of repeating myself, let's just do the first pass which is > to switch virtio over to always using the DMA API in the actual data > flow code, with a hook at initialization time that replaces the DMA ops > with some home cooked "direct" ops in the case where the IOMMU flag > isn't set. > > This will be equivalent to what we have today but avoids having 2 > separate code path all over the driver. > > Then a second stage, I think, is to replace this "hook" so that the > architecture gets a say in the matter. I don't think we can actually use dma_direct_ops. It still allows architectures to override parts of the dma setup, which virtio seems to blindly assume phys == dma and not cache flushing. I think the right way forward is to either add a new VIRTIO_F_IS_PCI_DEVICE (or redefine the existing iommu flag if deemed possible). And then make sure recent qemu always sets it.