[PATCH V2 1/2] powerpc/vas: Report proper error code for address translation failure

[Haren Myneni]

P9 DD2 NX workbook (Table 4-36) says DMA controller uses CC=5
internally for translation fault handling. NX reserves CC=250 for
OS to notify user space when NX encounters address translation
failure on the request buffer. Not an issue in earlier releases
as NX does not get faults on kernel addresses.

This patch defines CSB_CC_FAULT_ADDRESS(250) and updates CSB.CC with
this proper error code for user space.

Signed-off-by: Haren Myneni <ha...@linux.ibm.com>

Changes in V2:
- Use CSB_CC_FAULT_ADDRESS instead of CSB_CC_ADDRESS_TRANSLATION
  to distinguish from other error codes.
- Add NX workbook reference in the comment.

---
 Documentation/powerpc/vas-api.rst          | 2 +-
 arch/powerpc/include/asm/icswx.h           | 4 ++++
 arch/powerpc/platforms/powernv/vas-fault.c | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/powerpc/vas-api.rst 
b/Documentation/powerpc/vas-api.rst
index 1217c2f..788dc83 100644
--- a/Documentation/powerpc/vas-api.rst
+++ b/Documentation/powerpc/vas-api.rst
@@ -213,7 +213,7 @@ request buffers are not in memory. The operating system 
handles the fault by
 updating CSB with the following data:
 
        csb.flags = CSB_V;
-       csb.cc = CSB_CC_TRANSLATION;
+       csb.cc = CSB_CC_FAULT_ADDRESS;
        csb.ce = CSB_CE_TERMINATION;
        csb.address = fault_address;
 
diff --git a/arch/powerpc/include/asm/icswx.h b/arch/powerpc/include/asm/icswx.h
index 965b1f3..9bc7c58 100644
--- a/arch/powerpc/include/asm/icswx.h
+++ b/arch/powerpc/include/asm/icswx.h
@@ -77,6 +77,10 @@ struct coprocessor_completion_block {
 #define CSB_CC_CHAIN           (37)
 #define CSB_CC_SEQUENCE                (38)
 #define CSB_CC_HW              (39)
+/*
+ * P9 DD NX Workbook 3.2 (Table 4-36): Address translation fault
+ */
+#define        CSB_CC_FAULT_ADDRESS    (250)
 
 #define CSB_SIZE               (0x10)
 #define CSB_ALIGN              CSB_SIZE
diff --git a/arch/powerpc/platforms/powernv/vas-fault.c 
b/arch/powerpc/platforms/powernv/vas-fault.c
index 266a6ca..3d21fce 100644
--- a/arch/powerpc/platforms/powernv/vas-fault.c
+++ b/arch/powerpc/platforms/powernv/vas-fault.c
@@ -79,7 +79,7 @@ static void update_csb(struct vas_window *window,
        csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
 
        memset(&csb, 0, sizeof(csb));
-       csb.cc = CSB_CC_TRANSLATION;
+       csb.cc = CSB_CC_FAULT_ADDRESS;
        csb.ce = CSB_CE_TERMINATION;
        csb.cs = 0;
        csb.count = 0;
-- 
1.8.3.1