aspeed: Create flash devices only when defaults are enabled

When the -nodefaults option is set, flash devices should be created
with :

    -blockdev node-name=fmc0,driver=file,filename=./flash.img \
    -device mx66u51235f,cs=0x0,bus=ssi.0,drive=fmc0 \

To be noted that in this case, the ROM will not be installed and the
initial boot sequence (U-Boot loading) will fetch instructions using
SPI transactions which is significantly slower. That's exactly how HW
operates though.

Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

docs/system/arm/aspeed.rst

@@ -104,7 +104,7 @@ To boot a kernel directly from a Linux build tree:
         -dtb arch/arm/boot/dts/aspeed-ast2600-evb.dtb \
         -initrd rootfs.cpio
 
-The image should be attached as an MTD drive. Run :
+To boot the machine from the flash image, use an MTD drive :
 
 .. code-block:: bash
 
@@ -117,23 +117,46 @@ Options specific to Aspeed machines are :
    device by using the FMC controller to load the instructions, and
    not simply from RAM. This takes a little longer.
 
- * ``fmc-model`` to change the FMC Flash model. FW needs support for
+ * ``fmc-model`` to change the default FMC Flash model. FW needs
-   the chip model to boot.
+   support for the chip model to boot.
 
- * ``spi-model`` to change the SPI Flash model.
+ * ``spi-model`` to change the default SPI Flash model.
 
  * ``bmc-console`` to change the default console device. Most of the
    machines use the ``UART5`` device for a boot console, which is
    mapped on ``/dev/ttyS4`` under Linux, but it is not always the
    case.
 
-For instance, to start the ``ast2500-evb`` machine with a different
+To use other flash models, for instance a different FMC chip and a
-FMC chip and a bigger (64M) SPI chip, use :
+bigger (64M) SPI for the ``ast2500-evb`` machine, run :
 
 .. code-block:: bash
 
   -M ast2500-evb,fmc-model=mx25l25635e,spi-model=mx66u51235f
 
+When more flexibility is needed to define the flash devices, to use
+different flash models or define all flash devices (up to 8), the
+``-nodefaults`` QEMU option can be used to avoid creating the default
+flash devices.
+
+Flash devices should then be created from the command line and attached
+to a block device :
+
+.. code-block:: bash
+
+  $ qemu-system-arm -M ast2600-evb \
+        -blockdev node-name=fmc0,driver=file,filename=/path/to/fmc0.img \
+	-device mx66u51235f,bus=ssi.0,cs=0x0,drive=fmc0 \
+	-blockdev node-name=fmc1,driver=file,filename=/path/to/fmc1.img \
+	-device mx66u51235f,bus=ssi.0,cs=0x1,drive=fmc1 \
+	-blockdev node-name=spi1,driver=file,filename=/path/to/spi1.img \
+	-device mx66u51235f,cs=0x0,bus=ssi.1,drive=spi1 \
+	-nographic -nodefaults
+
+In that case, the machine boots fetching instructions from the FMC0
+device. It is slower to start but closer to what HW does. Using the
+machine option ``execute-in-place`` has a similar effect.
+
 To change the boot console and use device ``UART3`` (``/dev/ttyS2``
 under Linux), use :
 

hw/arm/aspeed.c

@@ -396,12 +396,14 @@ static void aspeed_machine_init(MachineState *machine)
     connect_serial_hds_to_uarts(bmc);
     qdev_realize(DEVICE(&bmc->soc), NULL, &error_abort);
 
-    aspeed_board_init_flashes(&bmc->soc.fmc,
+    if (defaults_enabled()) {
+        aspeed_board_init_flashes(&bmc->soc.fmc,
                               bmc->fmc_model ? bmc->fmc_model : amc->fmc_model,
                               amc->num_cs, 0);
-    aspeed_board_init_flashes(&bmc->soc.spi[0],
+        aspeed_board_init_flashes(&bmc->soc.spi[0],
                               bmc->spi_model ? bmc->spi_model : amc->spi_model,
                               1, amc->num_cs);
+    }
 
     if (machine->kernel_filename && sc->num_cpus > 1) {
         /* With no u-boot we must set up a boot stub for the secondary CPU */