[PATCH v2 4/5] memory-device: Add get_min_alignment() callback

[David Hildenbrand]

Add a callback that can be used to express additional alignment
requirements (exceeding the ones from the memory region).

Will be used by virtio-mem to express special alignment requirements due
to manually configured, big block sizes (e.g., 1GB with an ordinary
memory-backend-ram). This avoids failing later when realizing, because
auto-detection wasn't able to assign a properly aligned address.

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/mem/memory-device.c         | 11 +++++++++--
 include/hw/mem/memory-device.h | 10 ++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
index 8a736f1a26..cf0627fd01 100644
--- a/hw/mem/memory-device.c
+++ b/hw/mem/memory-device.c
@@ -259,7 +259,7 @@ void memory_device_pre_plug(MemoryDeviceState *md, 
MachineState *ms,
 {
     const MemoryDeviceClass *mdc = MEMORY_DEVICE_GET_CLASS(md);
     Error *local_err = NULL;
-    uint64_t addr, align;
+    uint64_t addr, align = 0;
     MemoryRegion *mr;
 
     mr = mdc->get_memory_region(md, &local_err);
@@ -267,7 +267,14 @@ void memory_device_pre_plug(MemoryDeviceState *md, 
MachineState *ms,
         goto out;
     }
 
-    align = legacy_align ? *legacy_align : memory_region_get_alignment(mr);
+    if (legacy_align) {
+        align = *legacy_align;
+    } else {
+        if (mdc->get_min_alignment) {
+            align = mdc->get_min_alignment(md);
+        }
+        align = MAX(align, memory_region_get_alignment(mr));
+    }
     addr = mdc->get_addr(md);
     addr = memory_device_get_free_addr(ms, !addr ? NULL : &addr, align,
                                        memory_region_size(mr), &local_err);
diff --git a/include/hw/mem/memory-device.h b/include/hw/mem/memory-device.h
index cde52e83c9..dcef8d65f7 100644
--- a/include/hw/mem/memory-device.h
+++ b/include/hw/mem/memory-device.h
@@ -88,6 +88,16 @@ struct MemoryDeviceClass {
      */
     MemoryRegion *(*get_memory_region)(MemoryDeviceState *md, Error **errp);
 
+    /*
+     * Optional: Return the desired minimum alignment of the device in guest
+     * physical address space. The final alignment is computed based on this
+     * alignment and the alignment requirements of the memory region.
+     *
+     * Called when plugging the memory device to detect the required alignment
+     * during address assignment.
+     */
+    uint64_t (*get_min_alignment)(const MemoryDeviceState *md);
+
     /*
      * Translate the memory device into #MemoryDeviceInfo.
      */
-- 
2.26.2