[PATCH v2 2/4] iommu/omap: Play nice in multi-platform builds

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

From: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>

The OMAP IOMMU driver unconditionally executes code and registers a
struct iommu_ops with the platform bus irrespective of whether it runs
on an OMAP SoC or not. This causes problems in multi-platform kernels
where drivers for other SoCs will no longer be able to register their
own struct iommu_ops or even try to use a struct iommu_ops for an IOMMU
that obviously isn't there.

The smallest fix I could think of is to check for the existence of any
OMAP IOMMU devices in the device tree and skip initialization otherwise.

This fixes a problem on Tegra20 where the DRM driver will try to use the
obviously non-existent OMAP IOMMU.

Reported-by: Nicolas Chauvet <kwizart-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>
Cc: Suman Anna <s-anna-l0cyMroinI0@public.gmane.org>
Cc: Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>
Signed-off-by: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
---
Changes in v2:
- do not fix up module exit function since it's dead code
- drop reference to struct device_node

 drivers/iommu/omap-iommu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/iommu/omap-iommu.c b/drivers/iommu/omap-iommu.c
index f59f857b702e..a4ba851825c2 100644
--- a/drivers/iommu/omap-iommu.c
+++ b/drivers/iommu/omap-iommu.c
@@ -1376,6 +1376,13 @@ static int __init omap_iommu_init(void)
 	struct kmem_cache *p;
 	const unsigned long flags = SLAB_HWCACHE_ALIGN;
 	size_t align = 1 << 10; /* L2 pagetable alignement */
+	struct device_node *np;
+
+	np = of_find_matching_node(NULL, omap_iommu_of_match);
+	if (!np)
+		return 0;
+
+	of_node_put(np);
 
 	p = kmem_cache_create("iopte_cache", IOPTE_TABLE_SIZE, align, flags,
 			      iopte_cachep_ctor);
-- 
2.1.3