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Date:   Wed, 9 Sep 2020 08:06:20 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Tom Murphy <murphyt7@tcd.ie>, intel-gfx@lists.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        iommu@lists.linux-foundation.org,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH V2 5/5] DO NOT MERGE: iommu: disable list appending in
 dma-iommu
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On Wed, Sep 09, 2020 at 09:43:09AM +0800, Lu Baolu wrote:
> +       /*
> +        * The Intel graphic device driver is used to assume that the
> returned
> +        * sg list is not combound. This blocks the efforts of converting
> the

This adds pointless overly long lines.

> +        * Intel IOMMU driver to dma-iommu api's. Add this quirk to make the
> +        * device driver work and should be removed once it's fixed in i915
> +        * driver.
> +        */
> +       if (dev_is_pci(dev) &&
> +           to_pci_dev(dev)->vendor == PCI_VENDOR_ID_INTEL &&
> +           (to_pci_dev(dev)->class >> 16) == PCI_BASE_CLASS_DISPLAY) {
> +               for_each_sg(sg, s, nents, i) {
> +                       unsigned int s_iova_off = sg_dma_address(s);
> +                       unsigned int s_length = sg_dma_len(s);
> +                       unsigned int s_iova_len = s->length;
> +
> +                       s->offset += s_iova_off;
> +                       s->length = s_length;
> +                       sg_dma_address(s) = dma_addr + s_iova_off;
> +                       sg_dma_len(s) = s_length;
> +                       dma_addr += s_iova_len;
> +               }
> +
> +               return nents;
> +       }

This wants an IS_ENABLED() check.  And probably a pr_once reminding
of the workaround.