From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH v5 1/1] iommu-api: Add map_sg/unmap_sg functions Date: Tue, 19 Aug 2014 13:59:54 +0200 Message-ID: <20140819115954.GC16329@8bytes.org> References: <1407797150-515-1-git-send-email-ohaugan@codeaurora.org> <1407797150-515-2-git-send-email-ohaugan@codeaurora.org> <20140818215553.GJ9809@8bytes.org> <53F2829C.2040809@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <53F2829C.2040809-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> 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: Olav Haugan Cc: laurent.pinchart+renesas-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org, linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Varun.Sethi-KZfg59tc24xl57MIdRCFDg@public.gmane.org, kgene.kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org, dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-arm-msm@vger.kernel.org On Mon, Aug 18, 2014 at 03:47:56PM -0700, Olav Haugan wrote: > If the alignment is not correct then iommu_map() will return error. Not > sure what other option we have here (and why make it different behavior > than iommu_map which just return error when it is not aligned properly). > I don't think we want to force any kind of alignment automatically. I > would rather have the API tell me I am doing something wrong than having > the function aligning the values and possibly undermap or overmap. But sg->offset is an offset into the page (at least it is used that way in the DMA-API and since you do 'page_len = s->offset + s->length' you use it the same way). So when you pass iova + offset the result will no longer be page-aligned. You should force sg->offset == 0 and sg->length to be page-aligned instead. This makes more sense because the IOMMU-API works on (io)-page granularity and not on arbitrary phys-addr ranges like the DMA-API. > Yes, I am aware of that. However, several people prefer this than > passing in scatterlist. It is not very convenient to pass a scatterlist > in some use cases. Someone mentioned a use case where they would have to > create a dummy sg list and populate it with the iova just to do an > unmap. I believe we would have to do this also. There is no use for > sglist when unmapping. However, would like to keep separate API from > iommu_unmap() to keep the API function names symmetric (map_sg/unmap_sg). Keeping it symetric is not more complicated, the caller just needs to keep the sg-list used for mapping around. I prefer the unmap_sg call to work in sg-lists too. > I thought that was why we added the default fallback and set all the > drivers to point to these fallback functions. Several people wanted this > so that we don't have to have NULL-check in these functions (and have > the functions be simple inline functions). Okay, since you add these call-backs to all drivers I think I can live with not doing a pointer check here. Joerg From mboxrd@z Thu Jan 1 00:00:00 1970 From: joro@8bytes.org (Joerg Roedel) Date: Tue, 19 Aug 2014 13:59:54 +0200 Subject: [PATCH v5 1/1] iommu-api: Add map_sg/unmap_sg functions In-Reply-To: <53F2829C.2040809@codeaurora.org> References: <1407797150-515-1-git-send-email-ohaugan@codeaurora.org> <1407797150-515-2-git-send-email-ohaugan@codeaurora.org> <20140818215553.GJ9809@8bytes.org> <53F2829C.2040809@codeaurora.org> Message-ID: <20140819115954.GC16329@8bytes.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Aug 18, 2014 at 03:47:56PM -0700, Olav Haugan wrote: > If the alignment is not correct then iommu_map() will return error. Not > sure what other option we have here (and why make it different behavior > than iommu_map which just return error when it is not aligned properly). > I don't think we want to force any kind of alignment automatically. I > would rather have the API tell me I am doing something wrong than having > the function aligning the values and possibly undermap or overmap. But sg->offset is an offset into the page (at least it is used that way in the DMA-API and since you do 'page_len = s->offset + s->length' you use it the same way). So when you pass iova + offset the result will no longer be page-aligned. You should force sg->offset == 0 and sg->length to be page-aligned instead. This makes more sense because the IOMMU-API works on (io)-page granularity and not on arbitrary phys-addr ranges like the DMA-API. > Yes, I am aware of that. However, several people prefer this than > passing in scatterlist. It is not very convenient to pass a scatterlist > in some use cases. Someone mentioned a use case where they would have to > create a dummy sg list and populate it with the iova just to do an > unmap. I believe we would have to do this also. There is no use for > sglist when unmapping. However, would like to keep separate API from > iommu_unmap() to keep the API function names symmetric (map_sg/unmap_sg). Keeping it symetric is not more complicated, the caller just needs to keep the sg-list used for mapping around. I prefer the unmap_sg call to work in sg-lists too. > I thought that was why we added the default fallback and set all the > drivers to point to these fallback functions. Several people wanted this > so that we don't have to have NULL-check in these functions (and have > the functions be simple inline functions). Okay, since you add these call-backs to all drivers I think I can live with not doing a pointer check here. Joerg