iommu/rockchip: Play nice in multi-platform builds

The Rockchip IOMMU driver unconditionally executes code and registers a
struct iommu_ops with the platform bus irrespective of whether it runs
on a Rockchip 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
Rockchip 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 Rockchip IOMMU.

Reported-by: Nicolas Chauvet <kwizart@gmail.com>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index 6a8b1ec4a48a..9f74fddcd304 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -1015,8 +1015,15 @@ static struct platform_driver rk_iommu_driver = {
 
 static int __init rk_iommu_init(void)
 {
+        struct device_node *np;
         int ret;
 
+        np = of_find_matching_node(NULL, rk_iommu_dt_ids);
+        if (!np)
+                return 0;
+
+        of_node_put(np);
+
         ret = bus_set_iommu(&platform_bus_type, &rk_iommu_ops);
         if (ret)
                 return ret;