[PATCH 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>
---
 drivers/iommu/omap-iommu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/iommu/omap-iommu.c b/drivers/iommu/omap-iommu.c
index bbb7dcef02d3..e4d4f133a3b3 100644
--- a/drivers/iommu/omap-iommu.c
+++ b/drivers/iommu/omap-iommu.c
@@ -1377,6 +1377,9 @@ static int __init omap_iommu_init(void)
 	const unsigned long flags = SLAB_HWCACHE_ALIGN;
 	size_t align = 1 << 10; /* L2 pagetable alignement */
 
+	if (!of_find_matching_node(NULL, omap_iommu_of_match))
+		return 0;
+
 	p = kmem_cache_create("iopte_cache", IOPTE_TABLE_SIZE, align, flags,
 			      iopte_cachep_ctor);
 	if (!p)
@@ -1394,6 +1397,9 @@ subsys_initcall(omap_iommu_init);
 
 static void __exit omap_iommu_exit(void)
 {
+	if (!of_find_matching_node(NULL, omap_iommu_of_match))
+		return;
+
 	kmem_cache_destroy(iopte_cachep);
 
 	platform_driver_unregister(&omap_iommu_driver);
-- 
2.1.3