linux-kernel - Re: [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api

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Date:   Thu, 27 Aug 2020 15:36:16 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Tom Murphy <murphyt7@....ie>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@...radead.org>,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Julien Grall <julien.grall@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-samsung-soc@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-rockchip@...ts.infradead.org, Andy Gross <agross@...nel.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        linux-s390@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org,
        Alex Williamson <alex.williamson@...hat.com>,
        linux-mediatek@...ts.infradead.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        linux-tegra@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org,
        Robin Murphy <robin.murphy@....com>,
        Cornelia Huck <cohuck@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kukjin Kim <kgene@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
Subject: Re: [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api



On 2020-08-23 6:04 p.m., Tom Murphy wrote:
> I have added a check for the sg_dma_len == 0 :
> """
>  } __sgt_iter(struct scatterlist *sgl, bool dma) {
>         struct sgt_iter s = { .sgp = sgl };
> 
> +       if (sgl && sg_dma_len(sgl) == 0)
> +           s.sgp = NULL;
> 
>         if (s.sgp) {
>             .....
> """
> at location [1].
> but it doens't fix the problem.

Based on my read of the code, it looks like we also need to change usage
of sgl->length... Something like the rough patch below, maybe?

Also, Tom, do you have an updated version of the patchset to convert the
Intel IOMMU to dma-iommu available? The last one I've found doesn't
apply cleanly (I'm assuming parts of it have been merged in slightly
modified forms).

Thanks,

Logan

--

diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
b/drivers/gpu/drm/i915/i915
index b7b59328cb76..9367ac801f0c 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h
@@ -27,13 +27,19 @@ static __always_inline struct sgt_iter {
 } __sgt_iter(struct scatterlist *sgl, bool dma) {
        struct sgt_iter s = { .sgp = sgl };

+       if (sgl && !sg_dma_len(s.sgp))
+               s.sgp = NULL;
+
        if (s.sgp) {
                s.max = s.curr = s.sgp->offset;
-               s.max += s.sgp->length;
-               if (dma)
+
+               if (dma) {
+                       s.max += sg_dma_len(s.sgp);
                        s.dma = sg_dma_address(s.sgp);
-               else
+               } else {
+                       s.max += s.sgp->length;
                        s.pfn = page_to_pfn(sg_page(s.sgp));
+               }
        }

        return s;