Will be used by virtio-mem to express special alignment requirements due
to manually configured, big block sizes. This avoids failing later when
realizing, because auto-detection wasn't able to assign a properly
aligned address.

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 | 11 +++++++++++
 2 files changed, 20 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..563893854a 100644
--- a/include/hw/mem/memory-device.h
+++ b/include/hw/mem/memory-device.h
@@ -88,6 +88,17 @@ struct MemoryDeviceClass {
      */
     MemoryRegion *(*get_memory_region)(MemoryDeviceState *md, Error **errp);
 
+    /*
+     * Optional: Return the desired minimum alignment of the device in guest
+     * physical address space, ignoring the alignment requirements of the
+     * memory region (e.g., based on the page size). The final alignment is
+     * computed by selecting the maximum of both alignments.
+     *
+     * 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

> Will be used by virtio-mem to express special alignment requirements due
> to manually configured, big block sizes. This avoids failing later when
> realizing, because auto-detection wasn't able to assign a properly
> aligned address.
>
> 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 | 11 +++++++++++
>  2 files changed, 20 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..563893854a 100644
> --- a/include/hw/mem/memory-device.h
> +++ b/include/hw/mem/memory-device.h
> @@ -88,6 +88,17 @@ struct MemoryDeviceClass {
>       */
>      MemoryRegion *(*get_memory_region)(MemoryDeviceState *md, Error **errp);
>
> +    /*
> +     * Optional: Return the desired minimum alignment of the device in guest
> +     * physical address space, ignoring the alignment requirements of the
> +     * memory region (e.g., based on the page size). The final alignment is
> +     * computed by selecting the maximum of both alignments.
> +     *
> +     * 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.
>       */
> --

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>