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

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Message-ID: <CALQxJuuS8KKUX_eWWSE81gsq5ePAETB-FoqRUSWFfqgr+B13gg@mail.gmail.com>
Date:   Fri, 28 Aug 2020 00:34:41 +0100
From:   Tom Murphy <murphyt7@....ie>
To:     Logan Gunthorpe <logang@...tatee.com>
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 Thu, 27 Aug 2020 at 22:36, Logan Gunthorpe <logang@...tatee.com> wrote:
>
>
>
> 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).
>

I'll try and post one in the next 24hours

> 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;