From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 08/20] powerpc/dma: remove the unused dma_nommu_ops export Date: Wed, 22 Aug 2018 08:45:31 +0200 Message-ID: <20180822064531.GA19284@lst.de> References: <20180730163824.10064-1-hch@lst.de> <20180730163824.10064-9-hch@lst.de> <20180731121625.GA29793@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Benjamin Herrenschmidt Cc: Fenghua Yu , Tony Luck , linux-ia64-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Konrad Rzeszutek Wilk , Michael Ellerman , Robin Murphy , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Paul Mackerras , linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Christoph Hellwig List-Id: iommu@lists.linux-foundation.org On Thu, Aug 09, 2018 at 10:01:16AM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote: > > It turns out cxl actually uses it. So for now skip this patch, > > although random code in drivers messing with dma ops will need to > > be sorted out sooner or later. > > CXL devices are "special", they bypass the classic iommu in favor of > allowing the device to operate using the main processor page tables > using an MMU context (so basically the device can use userspace > addresses directly), akin to ATS. > > I think the code currently uses the nommu ops as a way to do a simple > kernel mapping for kernel drivers using CXL (not userspace stuff) > though. Its still a horrible idea to have this in drivers/, we need some core API to mediate this behavior. Also if the device supports using virtual addresses dma_nommu_ops seems wrong as it won't do the right thing for e.g. vmalloc addresses not mapped into the kernel linear mapping (which I guess can't currently happen on powerpc, but still..)