[PATCH v3 3/3] spapr: nvdimm: Enable sync-dax device property for nvdimm

[Shivaprasad G Bhat <sbhat@linux.ibm.com>]

The patch adds the 'sync-dax' property to the nvdimm device.

When the sync-dax is 'off', the device tree property
"hcall-flush-required" is added to the nvdimm node which makes the
guest to issue H_SCM_FLUSH hcalls to request for flushes explicitly.
This would be the default behaviour without sync-dax property set
for the nvdimm device.

The sync-dax="on" would mean the guest need not make flush requests
to the qemu. On previous machine versions the sync-dax is set to be
"on" by default using the hw_compat magic.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
---
 hw/core/machine.c       |    1 +
 hw/mem/nvdimm.c         |    1 +
 hw/ppc/spapr_nvdimm.c   |   17 +++++++++++++++++
 include/hw/mem/nvdimm.h |   10 ++++++++++
 include/hw/ppc/spapr.h  |    1 +
 5 files changed, 30 insertions(+)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 257a664ea2..f843643574 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -41,6 +41,7 @@ GlobalProperty hw_compat_5_2[] = {
     { "PIIX4_PM", "smm-compat", "on"},
     { "virtio-blk-device", "report-discard-granularity", "off" },
     { "virtio-net-pci", "vectors", "3"},
+    { "nvdimm", "sync-dax", "on" },
 };
 const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
 
diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
index 7397b67156..8f0e29b191 100644
--- a/hw/mem/nvdimm.c
+++ b/hw/mem/nvdimm.c
@@ -229,6 +229,7 @@ static void nvdimm_write_label_data(NVDIMMDevice *nvdimm, const void *buf,
 
 static Property nvdimm_properties[] = {
     DEFINE_PROP_BOOL(NVDIMM_UNARMED_PROP, NVDIMMDevice, unarmed, false),
+    DEFINE_PROP_BOOL(NVDIMM_SYNC_DAX_PROP, NVDIMMDevice, sync_dax, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
index 883317c1ed..dd1c90251b 100644
--- a/hw/ppc/spapr_nvdimm.c
+++ b/hw/ppc/spapr_nvdimm.c
@@ -125,6 +125,9 @@ static int spapr_dt_nvdimm(SpaprMachineState *spapr, void *fdt,
     uint64_t lsize = nvdimm->label_size;
     uint64_t size = object_property_get_int(OBJECT(nvdimm), PC_DIMM_SIZE_PROP,
                                             NULL);
+    bool sync_dax = object_property_get_bool(OBJECT(nvdimm),
+                                             NVDIMM_SYNC_DAX_PROP,
+                                             &error_abort);
 
     drc = spapr_drc_by_id(TYPE_SPAPR_DRC_PMEM, slot);
     g_assert(drc);
@@ -159,6 +162,11 @@ static int spapr_dt_nvdimm(SpaprMachineState *spapr, void *fdt,
                              "operating-system")));
     _FDT(fdt_setprop(fdt, child_offset, "ibm,cache-flush-required", NULL, 0));
 
+    if (!sync_dax) {
+        _FDT(fdt_setprop(fdt, child_offset, "ibm,hcall-flush-required",
+                         NULL, 0));
+    }
+
     return child_offset;
 }
 
@@ -567,10 +575,12 @@ static target_ulong h_scm_flush(PowerPCCPU *cpu, SpaprMachineState *spapr,
                                       target_ulong opcode, target_ulong *args)
 {
     int ret;
+    bool sync_dax;
     uint32_t drc_index = args[0];
     uint64_t continue_token = args[1];
     SpaprDrc *drc = spapr_drc_by_index(drc_index);
     PCDIMMDevice *dimm;
+    NVDIMMDevice *nvdimm;
     HostMemoryBackend *backend = NULL;
     SpaprNVDIMMDeviceFlushState *state;
     ThreadPool *pool = aio_get_thread_pool(qemu_get_aio_context());
@@ -580,6 +590,13 @@ static target_ulong h_scm_flush(PowerPCCPU *cpu, SpaprMachineState *spapr,
         return H_PARAMETER;
     }
 
+    nvdimm = NVDIMM(drc->dev);
+    sync_dax = object_property_get_bool(OBJECT(nvdimm), NVDIMM_SYNC_DAX_PROP,
+                                        &error_abort);
+    if (sync_dax) {
+        return H_UNSUPPORTED;
+    }
+
     if (continue_token != 0) {
         ret = spapr_nvdimm_get_flush_status(continue_token);
         if (H_IS_LONG_BUSY(ret)) {
diff --git a/include/hw/mem/nvdimm.h b/include/hw/mem/nvdimm.h
index bcf62f825c..f82979cf2f 100644
--- a/include/hw/mem/nvdimm.h
+++ b/include/hw/mem/nvdimm.h
@@ -51,6 +51,7 @@ OBJECT_DECLARE_TYPE(NVDIMMDevice, NVDIMMClass, NVDIMM)
 #define NVDIMM_LABEL_SIZE_PROP "label-size"
 #define NVDIMM_UUID_PROP       "uuid"
 #define NVDIMM_UNARMED_PROP    "unarmed"
+#define NVDIMM_SYNC_DAX_PROP   "sync-dax"
 
 struct NVDIMMDevice {
     /* private */
@@ -85,6 +86,15 @@ struct NVDIMMDevice {
      */
     bool unarmed;
 
+    /*
+     * On PPC64,
+     * The 'off' value results in the hcall-flush-required property set
+     * in the device tree for pseries machines. When 'off', the guest
+     * initiates explicit flush requests to the backend device ensuring
+     * write persistence.
+     */
+    bool sync_dax;
+
     /*
      * The PPC64 - spapr requires each nvdimm device have a uuid.
      */
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 7c27fb3e2d..51c35488a4 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -333,6 +333,7 @@ struct SpaprMachineState {
 #define H_P7              -60
 #define H_P8              -61
 #define H_P9              -62
+#define H_UNSUPPORTED     -67
 #define H_OVERLAP         -68
 #define H_UNSUPPORTED_FLAG -256
 #define H_MULTI_THREADS_ACTIVE -9005