[PATCH v2 3/3] drm/msm: detach the ARM DMA mapping before attaching our own domain

On ARM32 with CONFIG_ARM_DMA_USE_IOMMU, arch_setup_dma_ops() creates a
dma_iommu_mapping for every IOMMU-backed device and attaches its domain
to the device's IOMMU group. That domain is neither the group's default
nor its blocking domain, so when msm_iommu_new() later attaches the
domain the driver manages itself, __iommu_attach_group() refuses it:

	if (group->domain && group->domain != group->default_domain &&
	    group->domain != group->blocking_domain)
		return -EBUSY;

Both the GPU and the display controller are hit by this on apq8064
(IFC6410), leaving the board with no GPU and no display:

  adreno 4300000.gpu: failed to load adreno gpu
  adreno 4300000.gpu: probe with driver adreno failed with error -16
  mdp4 5100000.display-controller: [drm:msm_drm_kms_init] *ERROR* failed to load kms
  mdp4 5100000.display-controller: adev bind failed: -16

Other ARM32 DRM drivers that manage their own domains (tegra, rockchip,
exynos) drop the arch mapping first. Do the same in msm_iommu_new(),
which both the display and the GPU paths go through.

With this the GPU and the KMS device both initialise:

  [drm] Initialized msm 1.13.0 for 4300000.gpu on minor 0
  [drm] Initialized msm-kms 1.13.0 for 5100000.display-controller on minor 1

Assisted-by: Claude:claude-opus-5
Reviewed-by: Konrad Dybcio <[email protected]>
Signed-off-by: Dmitry Baryshkov <[email protected]>
---
 drivers/gpu/drm/msm/msm_iommu.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
index 897e42c8d5c8..da6782fca6bd 100644
--- a/drivers/gpu/drm/msm/msm_iommu.c
+++ b/drivers/gpu/drm/msm/msm_iommu.c
@@ -7,6 +7,15 @@
 #include <linux/adreno-smmu-priv.h>
 #include <linux/io-pgtable.h>
 #include <linux/kmemleak.h>
+
+#if defined(CONFIG_ARM_DMA_USE_IOMMU)
+#include <asm/dma-iommu.h>
+#else
+#define arm_iommu_detach_device(...)	({ })
+#define arm_iommu_release_mapping(...)	({ })
+#define to_dma_iommu_mapping(dev)	NULL
+#endif
+
 #include "msm_drv.h"
 #include "msm_gpu_trace.h"
 #include "msm_mmu.h"
@@ -749,6 +758,19 @@ struct msm_mmu *msm_iommu_new(struct device *dev, unsigned long quirks)
 
 	mutex_init(&iommu->init_lock);
 
+	/*
+	 * ARM32 attaches a DMA mapping domain to every IOMMU-backed device,
+	 * which would make attaching our own domain fail with -EBUSY.
+	 */
+	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)) {
+		struct dma_iommu_mapping *mapping = to_dma_iommu_mapping(dev);
+
+		if (mapping) {
+			arm_iommu_detach_device(dev);
+			arm_iommu_release_mapping(mapping);
+		}
+	}
+
 	ret = iommu_attach_device(iommu->domain, dev);
 	if (ret) {
 		iommu_domain_free(domain);

-- 
2.47.3