[PATCH v6 24/27] x86: Add swiotlb force off support

[Yinghai Lu <yinghai@kernel.org>]

So use could disable swiotlb from command line, even swiotlb support
is compiled in.  Just like we have intel_iommu=on and intel_iommu=off.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
 Documentation/kernel-parameters.txt |    7 +++++++
 arch/x86/kernel/pci-swiotlb.c       |   10 +++++-----
 drivers/iommu/amd_iommu.c           |    1 +
 include/linux/swiotlb.h             |    1 +
 lib/swiotlb.c                       |    5 ++++-
 5 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 20e248c..08b4c9d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2832,6 +2832,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	swiotlb=	[IA-64] Number of I/O TLB slabs
 
+	swiotlb=[force|off|on] [KNL] disable or enable swiotlb.
+		force
+		on
+			Enable swiotlb.
+		off
+			Disable swiotlb.
+
 	switches=	[HW,M68k]
 
 	sysfs.deprecated=0|1 [KNL]
diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index 6f93eb7..80afd3b 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -58,12 +58,12 @@ static struct dma_map_ops swiotlb_dma_ops = {
  */
 int __init pci_swiotlb_detect_override(void)
 {
-	int use_swiotlb = swiotlb | swiotlb_force;
-
 	if (swiotlb_force)
 		swiotlb = 1;
+	else if (swiotlb_force_off)
+		swiotlb = 0;
 
-	return use_swiotlb;
+	return swiotlb;
 }
 IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
 		  pci_xen_swiotlb_detect,
@@ -76,9 +76,9 @@ IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
  */
 int __init pci_swiotlb_detect_4gb(void)
 {
-	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
+	/* don't initialize swiotlb if iommu=off (no_iommu=1) or force off */
 #ifdef CONFIG_X86_64
-	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
+	if (!no_iommu && !swiotlb_force_off && max_pfn > MAX_DMA32_PFN)
 		swiotlb = 1;
 #endif
 	return swiotlb;
diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 55074cb..4f370d3 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -3082,6 +3082,7 @@ int __init amd_iommu_init_dma_ops(void)
 	unhandled = device_dma_ops_init();
 	if (unhandled && max_pfn > MAX_DMA32_PFN) {
 		/* There are unhandled devices - initialize swiotlb for them */
+		WARN(swiotlb_force_off, "Please remove swiotlb=off\n");
 		swiotlb = 1;
 	}
 
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index f7535d1..dd7cf65 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -8,6 +8,7 @@ struct dma_attrs;
 struct scatterlist;
 
 extern int swiotlb_force;
+extern int swiotlb_force_off;
 
 /*
  * Maximum allowable number of contiguous slabs to map,
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 6b99ea7..3f51b2c 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -51,6 +51,7 @@
 #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
 
 int swiotlb_force;
+int swiotlb_force_off;
 
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
@@ -102,8 +103,10 @@ setup_io_tlb_npages(char *str)
 	}
 	if (*str == ',')
 		++str;
-	if (!strcmp(str, "force"))
+	if (!strcmp(str, "force") || !strcmp(str, "on"))
 		swiotlb_force = 1;
+	if (!strcmp(str, "off"))
+		swiotlb_force_off = 1;
 
 	return 1;
 }
-- 
1.7.10.4