linux-kernel - [PATCH 1/2] iommu - Enable debugfs exposure of the IOMMU

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Date:   Thu, 29 Mar 2018 17:54:44 -0500
From:   Gary R Hook <gary.hook@....com>
To:     iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, jacob.jun.pan@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] iommu - Enable debugfs exposure of the IOMMU

Provide base enablement for using debugfs to expose internal data of
an IOMMU driver. When enabled, create the /sys/kernel/debug/iommu
directory.  Emit a strong warning at boot time to indicate that this
feature is enabled.

Signed-off-by: Gary R Hook <gary.hook@....com>
---
 drivers/iommu/Kconfig          |   11 +++++++++++
 drivers/iommu/Makefile         |    2 ++
 drivers/iommu/amd_iommu_init.c |    2 ++
 drivers/iommu/iommu-debugfs.c  |   32 ++++++++++++++++++++++++++++++++
 include/linux/iommu.h          |    4 ++++
 5 files changed, 51 insertions(+)
 create mode 100644 drivers/iommu/iommu-debugfs.c

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index f3a21343e636..c1e39dabfec2 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
 
 endmenu
 
+config IOMMU_DEBUG
+	bool "Enable IOMMU internals in DebugFS"
+	depends on DEBUG_FS
+	default n
+	help
+	  Allows exposure of IOMMU device internals. This option enables
+	  the use of debugfs by IOMMU drivers as required. Devices can,
+	  at initialization time, cause the IOMMU code to create a top-level
+	  debug/iommu directory, and then populate a subdirectory with
+	  entries as required.
+
 config IOMMU_IOVA
 	tristate
 
diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index 1fb695854809..5e5c3339681d 100644
--- a/drivers/iommu/Makefile
+++ b/drivers/iommu/Makefile
@@ -2,6 +2,7 @@
 obj-$(CONFIG_IOMMU_API) += iommu.o
 obj-$(CONFIG_IOMMU_API) += iommu-traces.o
 obj-$(CONFIG_IOMMU_API) += iommu-sysfs.o
+obj-$(CONFIG_IOMMU_DEBUG) += iommu-debugfs.o
 obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
 obj-$(CONFIG_IOMMU_IO_PGTABLE) += io-pgtable.o
 obj-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
@@ -10,6 +11,7 @@ obj-$(CONFIG_IOMMU_IOVA) += iova.o
 obj-$(CONFIG_OF_IOMMU)	+= of_iommu.o
 obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
 obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o
+obj-$(CONFIG_AMD_IOMMU_DEBUG) += amd_iommu_debugfs.o
 obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
 obj-$(CONFIG_ARM_SMMU) += arm-smmu.o
 obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 6fe2d0346073..99d48c42a12f 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -2783,6 +2783,8 @@ int __init amd_iommu_detect(void)
 	iommu_detected = 1;
 	x86_init.iommu.iommu_init = amd_iommu_init;
 
+dump_stack();
+
 	return 1;
 }
 
diff --git a/drivers/iommu/iommu-debugfs.c b/drivers/iommu/iommu-debugfs.c
new file mode 100644
index 000000000000..94c9acc63b65
--- /dev/null
+++ b/drivers/iommu/iommu-debugfs.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD IOMMU driver
+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ *
+ * Author: Gary R Hook <gary.hook@....com>
+ */
+
+#include <linux/pci.h>
+#include <linux/iommu.h>
+#include <linux/debugfs.h>
+
+static struct dentry *iommu_debugfs_dir;
+
+#define	MAX_NAME_LEN	20
+
+/* Return a zero on failure; 1 on successful setup */
+struct dentry *iommu_debugfs_setup(void)
+{
+	if (!debugfs_initialized())
+		return NULL;
+
+	if (!iommu_debugfs_dir)
+		iommu_debugfs_dir = debugfs_create_dir("iommu", NULL);
+
+	if (iommu_debugfs_dir)
+		pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL\n");
+
+	return iommu_debugfs_dir;
+}
+EXPORT_SYMBOL_GPL(iommu_debugfs_setup);
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 41b8c5757859..cb2957dac43b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -696,6 +696,10 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
 	return NULL;
 }
 
+#ifdef	CONFIG_IOMMU_DEBUG
+struct dentry *iommu_debugfs_setup(void);
+#endif
+
 #endif /* CONFIG_IOMMU_API */
 
 #endif /* __LINUX_IOMMU_H */