drm/nouveau/platform: add IOMMU dependency

The recently added iommu code in the nouveau driver fails to build when the IOMMU support is disabled:

drivers/gpu/drm/nouveau/nouveau_platform.c: In function 'nouveau_platform_probe_iommu':
drivers/gpu/drm/nouveau/nouveau_platform.c:113:41: error: 'const struct iommu_ops' has no mem

To avoid the build error, this now adds an explicit dependency on the IOMMU implementation.

Signed-off-by Arnd Bergmann <[email protected]>

Fixes 58fd9375c2c5 ("drm/nouveau/platform: probe IOMMU if present")

The recently added iommu code in the nouveau driver fails to build when the IOMMU support is disabled:

drivers/gpu/drm/nouveau/nouveau_platform.c: In function 'nouveau_platform_probe_iommu':
drivers/gpu/drm/nouveau/nouveau_platform.c:113:41: error: 'const struct iommu_ops' has no mem

To avoid the build error, this now adds an explicit dependency on the IOMMU implementation.

The lack of IOMMU API support can make nouveau_platform_probe_iommu() fail to compile because struct iommu_ops is then empty. Fix this by skipping IOMMU probe in that case - lack of IOMMU on platform devices is sub-optimal, but is not an error.

Signed-off-by Alexandre Courbot <[email protected]>

---
This is an alternative to https://lkml.org/lkml/2015/5/19/484. Most users of Nouveau do not care about IOMMU support, so we should not impose that option on them.

Quoted 11 lines · On Wednesday 20 May 2015 15:10:24 Alexandre Courbot wrote:

The lack of IOMMU API support can make nouveau_platform_probe_iommu() fail to compile because struct iommu_ops is then empty. Fix this by skipping IOMMU probe in that case - lack of IOMMU on platform devices is sub-optimal, but is not an error.

Signed-off-by Alexandre Courbot <[email protected]>

---
This is an alternative to https://lkml.org/lkml/2015/5/19/484. Most users of Nouveau do not care about IOMMU support, so we should not impose that option on them.

Yes, good idea.

Acked-by Arnd Bergmann <[email protected]>

The lack of IOMMU API support can make nouveau_platform_probe_iommu() fail to compile because struct iommu_ops is then empty. Fix this by skipping IOMMU probe in that case - lack of IOMMU on platform devices is sub-optimal, but is not an error.

Signed-off-by Alexandre Courbot <[email protected]>

---
This is an alternative to https://lkml.org/lkml/2015/5/19/484. Most users of Nouveau do not care about IOMMU support, so we should not impose that option on them.

 drm/nouveau/nouveau_platform.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

drivers/gpu/drm/nouveau/nouveau_platform.c +6 -0

index 775277f1edb0..dcfbbfaf1739 100644
@@ -92,6 +92,8 @@ static int nouveau_platform_power_down(struct nouveau_platform_gpu *gpu)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_IOMMU_API)
+
 static void nouveau_platform_probe_iommu(struct device *dev,
 					 struct nouveau_platform_gpu *gpu)
 {

@@ -158,6 +160,20 @@ static void nouveau_platform_remove_iommu(struct device *dev,
 	}
 }
 
+#else
+
+static void nouveau_platform_probe_iommu(struct device *dev,
+					 struct nouveau_platform_gpu *gpu)

Since these are all static functions, perhaps an "if (IS_ENABLED(...))" would work here? That way you'd get compile coverage of the code in all cases.

But perhaps that doesn't work for IOMMU. I have a vague memory of running across something like this before and IOMMU has this quirk of defining struct iommu_ops as empty if IOMMU_API is deselected so you'll probably get compiler errors unless you actually preprocess the code out.

Quoted 4 lines · On Wednesday 20 May 2015 13:32:33 Thierry Reding wrote:

Since these are all static functions, perhaps an "if (IS_ENABLED(...))" would work here? That way you'd get compile coverage of the code in all cases.

I had the same thought at first.

Quoted 5 lines

But perhaps that doesn't work for IOMMU. I have a vague memory of running across something like this before and IOMMU has this quirk of defining struct iommu_ops as empty if IOMMU_API is deselected so you'll probably get compiler errors unless you actually preprocess the code out.

Exactly.