linux-kernel - [PATCH] iommu: Don't reserve IOVA when address and size are zero

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Date:   Thu, 23 Nov 2023 11:42:01 +0530
From:   Ashish Mhetre <amhetre@...dia.com>
To:     <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
        <robh@...nel.org>, <treding@...dia.com>
CC:     <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, Ashish Mhetre <amhetre@...dia.com>
Subject: [PATCH] iommu: Don't reserve IOVA when address and size are zero

When the bootloader/firmware doesn't setup the framebuffers, their
address and size are zero in "iommu-addresses" property. If we intend to
use display driver in kernel without framebuffer then it's causing
the display IOMMU mappings to fail as IOVA is reserved with size and
address as zero.
An ideal solution would be firmware removing the "iommu-addresses"
property and corresponding "memory-region" if display is not present.
But the kernel should be able to handle this by checking for size and
address of IOVA and skipping the IOVA reservation if both are 0.

Fixes: a5bf3cfce8cb ("iommu: Implement of_iommu_get_resv_regions()")
Signed-off-by: Ashish Mhetre <amhetre@...dia.com>
---
 drivers/iommu/of_iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index 157b286e36bf..150ef65d357a 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -255,6 +255,10 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
 				size_t length;

 				maps = of_translate_dma_region(np, maps, &iova, &length);
+				if (iova == 0 && length == 0) {
+					dev_dbg(dev, "Skipping IOVA reservation as address and size are zero\n");
+					continue;
+				}
 				type = iommu_resv_region_get_type(dev, &phys, iova, length);

 				region = iommu_alloc_resv_region(iova, length, prot, type,
-- 
2.17.1