[PATCH v2] virtio: kconfig: memory devices are PCI only

[Paolo Bonzini <pbonzini@redhat.com>]

Virtio memory devices rely on PCI BARs to expose the contents of memory.
Because of this they cannot be used (yet) with virtio-mmio or virtio-ccw.
In fact the code that is common to virtio-mem and virtio-pmem, which
is in hw/virtio/virtio-md-pci.c, is only included if CONFIG_VIRTIO_PCI
is set.  Reproduce the same condition in the Kconfig file, only allowing
VIRTIO_MEM and VIRTIO_PMEM to be defined if the transport supports it.

Without this patch it is possible to create a configuration with
CONFIG_VIRTIO_PCI=n and CONFIG_VIRTIO_MEM=y, but that causes a
linking failure.

Cc: David Hildenbrand <david@redhat.com>
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/virtio/Kconfig b/hw/virtio/Kconfig
index aa63ff7fd41..0afec2ae929 100644
--- a/hw/virtio/Kconfig
+++ b/hw/virtio/Kconfig
@@ -16,6 +16,7 @@ config VIRTIO_PCI
     default y if PCI_DEVICES
     depends on PCI
     select VIRTIO
+    select VIRTIO_MD_SUPPORTED
 
 config VIRTIO_MMIO
     bool
@@ -35,10 +36,17 @@ config VIRTIO_CRYPTO
     default y
     depends on VIRTIO
 
+# not all virtio transports support memory devices; if none does,
+# no need to include the code
+config VIRTIO_MD_SUPPORTED
+    bool
+
 config VIRTIO_MD
     bool
+    depends on VIRTIO_MD_SUPPORTED
     select MEM_DEVICE
 
+# selected by the board if it has the required support code
 config VIRTIO_PMEM_SUPPORTED
     bool
 
@@ -46,9 +54,11 @@ config VIRTIO_PMEM
     bool
     default y
     depends on VIRTIO
+    depends on VIRTIO_MD_SUPPORTED
     depends on VIRTIO_PMEM_SUPPORTED
     select VIRTIO_MD
 
+# selected by the board if it has the required support code
 config VIRTIO_MEM_SUPPORTED
     bool
 
@@ -57,6 +67,7 @@ config VIRTIO_MEM
     default y
     depends on VIRTIO
     depends on LINUX
+    depends on VIRTIO_MD_SUPPORTED
     depends on VIRTIO_MEM_SUPPORTED
     select VIRTIO_MD
 
-- 
2.46.0