x86/amd-iommu: Add reset function for command buffers

This patch factors parts of the command buffer
initialization code into a seperate function which can be
used to reset the command buffer later.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

2 files changed, 18 insertions, 5 deletions

diff --git a/arch/x86/include/asm/amd_iommu_types.h b/arch/x86/include/asm/amd_iommu_types.h
index 0c878caaa0a2..c54bc979dc17 100644
--- a/arch/x86/include/asm/amd_iommu_types.h
+++ b/arch/x86/include/asm/amd_iommu_types.h
@@ -457,4 +457,7 @@ static inline void amd_iommu_stats_init(void) { }
 
 #endif /* CONFIG_AMD_IOMMU_STATS */
 
+/* some function prototypes */
+extern void amd_iommu_reset_cmd_buffer(struct amd_iommu *iommu);
+
 #endif /* _ASM_X86_AMD_IOMMU_TYPES_H */
diff --git a/arch/x86/kernel/amd_iommu_init.c b/arch/x86/kernel/amd_iommu_init.c
index c1b17e97252e..1752afef948a 100644
--- a/arch/x86/kernel/amd_iommu_init.c
+++ b/arch/x86/kernel/amd_iommu_init.c
@@ -435,6 +435,20 @@ static u8 * __init alloc_command_buffer(struct amd_iommu *iommu)
 }
 
 /*
+ * This function resets the command buffer if the IOMMU stopped fetching
+ * commands from it.
+ */
+void amd_iommu_reset_cmd_buffer(struct amd_iommu *iommu)
+{
+        iommu_feature_disable(iommu, CONTROL_CMDBUF_EN);
+
+        writel(0x00, iommu->mmio_base + MMIO_CMD_HEAD_OFFSET);
+        writel(0x00, iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
+
+        iommu_feature_enable(iommu, CONTROL_CMDBUF_EN);
+}
+
+/*
  * This function writes the command buffer address to the hardware and
  * enables it.
  */
@@ -450,11 +464,7 @@ static void iommu_enable_command_buffer(struct amd_iommu *iommu)
         memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET,
                     &entry, sizeof(entry));
 
-        /* set head and tail to zero manually */
-        writel(0x00, iommu->mmio_base + MMIO_CMD_HEAD_OFFSET);
-        writel(0x00, iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
-
-        iommu_feature_enable(iommu, CONTROL_CMDBUF_EN);
+        amd_iommu_reset_cmd_buffer(iommu);
 }
 
 static void __init free_command_buffer(struct amd_iommu *iommu)