[PATCH] hw/mem: support zero memory size CXL device

[Hongjian Fan]

According to CXL 3.1 specification, 8.1.3.8 DVSEC CXL Range Registers "A 
CXL.mem-capable device is permitted to report zero memory size."
This patch will allow a CXL type3 device to be initialized with zero memory 
size, when there is no memory device property provided ( neither volatile, 
persistent, nor dynamic region).

Signed-off-by: Hongjian Fan <hongjian.fan@seagate.com>
---
 hw/mem/cxl_type3.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c
index 5cf754b38f..35caa186ca 100644
--- a/hw/mem/cxl_type3.c
+++ b/hw/mem/cxl_type3.c
@@ -159,7 +159,12 @@ static int ct3_build_cdat_table(CDATSubHeader 
***cdat_table, void *priv)
     int len = 0;
 
     if (!ct3d->hostpmem && !ct3d->hostvmem && !ct3d->dc.num_regions) {
-        return 0;
+        // zero memory size device. Build one entry with size 0
+        table = g_malloc0(CT3_CDAT_NUM_ENTRIES * sizeof(*table));
+        ct3_build_cdat_entries_for_mr(&(table[0]), dsmad_handle++,
+                                0, false, false, 0);
+        *cdat_table = g_steal_pointer(&table);
+        return CT3_CDAT_NUM_ENTRIES;
     }
 
     if (ct3d->hostvmem) {
@@ -712,8 +717,11 @@ static bool cxl_setup_memory(CXLType3Dev *ct3d, Error 
**errp)
 
     if (!ct3d->hostmem && !ct3d->hostvmem && !ct3d->hostpmem
         && !ct3d->dc.num_regions) {
-        error_setg(errp, "at least one memdev property must be set");
-        return false;
+        // no memdev property provided. Default to zero memory size device
+        ct3d->cxl_dstate.pmem_size = 0;
+        ct3d->cxl_dstate.vmem_size = 0;
+        ct3d->cxl_dstate.static_mem_size = 0;
+        return true;
     } else if (ct3d->hostmem && ct3d->hostpmem) {
         error_setg(errp, "[memdev] cannot be used with new "
                          "[persistent-memdev] property");
-- 
2.25.1