hw/misc: deprecate the 'sga' device

This is obsolete since SeaBIOS 1.11.0 introduced native support for
sending messages to the serial console. The new support can be
activated using -machine graphics=off on x86 targets.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20210909123219.862652-1-berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

docs/about/deprecated.rst

@@ -313,6 +313,16 @@ full SCSI support.  Use virtio-scsi instead when SCSI passthrough is required.
 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
 alias.
 
+``-device sga`` (since 6.2)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``sga`` device loads an option ROM for x86 targets which enables
+SeaBIOS to send messages to the serial console. SeaBIOS 1.11.0 onwards
+contains native support for this feature and thus use of the option
+ROM approach is obsolete. The native SeaBIOS support can be activated
+by using ``-machine graphics=off``.
+
+
 Block device options
 ''''''''''''''''''''
 

hw/misc/sga.c

@@ -30,6 +30,7 @@
 #include "hw/loader.h"
 #include "qemu/module.h"
 #include "qom/object.h"
+#include "qemu/error-report.h"
 
 #define SGABIOS_FILENAME "sgabios.bin"
 
@@ -42,6 +43,7 @@ struct ISASGAState {
 
 static void sga_realizefn(DeviceState *dev, Error **errp)
 {
+    warn_report("-device sga is deprecated, use -machine graphics=off");
     rom_add_vga(SGABIOS_FILENAME);
 }