aspeed: Introduce a "bmc-console" machine option

Most of the Aspeed machines use the UART5 device for the boot console,
and QEMU connects the first serial Chardev to this SoC device for this
purpose. See routine connect_serial_hds_to_uarts().

Nevertheless, some machines use another boot console, such as the fuji,
and commit 5d63d0c76c ("hw/arm/aspeed: Allow machine to set UART
default") introduced a SoC class attribute 'uart_default' and property
to be able to change the boot console device. It was later changed by
commit d2b3eaefb4 ("aspeed: Refactor UART init for multi-SoC machines").

The "bmc-console" machine option goes a step further and lets the user define
the UART device from the QEMU command line without introducing a new
machine definition. For instance, to use device UART3 (mapped on
/dev/ttyS2 under Linux) instead of the default UART5, one would use :

  -M ast2500-evb,bmc-console=uart3

Cc: Abhishek Singh Dagur <abhishek@drut.io>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

docs/system/arm/aspeed.rst

@@ -122,6 +122,11 @@ Options specific to Aspeed machines are :
 
  * ``spi-model`` to change the 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
 FMC chip and a bigger (64M) SPI chip, use :
 
@@ -129,6 +134,12 @@ FMC chip and a bigger (64M) SPI chip, use :
 
   -M ast2500-evb,fmc-model=mx25l25635e,spi-model=mx66u51235f
 
+To change the boot console and use device ``UART3`` (``/dev/ttyS2``
+under Linux), use :
+
+.. code-block:: bash
+
+  -M ast2500-evb,bmc-console=uart3
 
 Aspeed minibmc family boards (``ast1030-evb``)
 ==================================================================

hw/arm/aspeed.c

@@ -42,6 +42,7 @@ struct AspeedMachineState {
     AspeedSoCState soc;
     MemoryRegion boot_rom;
     bool mmio_exec;
+    uint32_t uart_chosen;
     char *fmc_model;
     char *spi_model;
 };
@@ -333,10 +334,11 @@ static void connect_serial_hds_to_uarts(AspeedMachineState *bmc)
     AspeedMachineClass *amc = ASPEED_MACHINE_GET_CLASS(bmc);
     AspeedSoCState *s = &bmc->soc;
     AspeedSoCClass *sc = ASPEED_SOC_GET_CLASS(s);
+    int uart_chosen = bmc->uart_chosen ? bmc->uart_chosen : amc->uart_default;
 
-    aspeed_soc_uart_set_chr(s, amc->uart_default, serial_hd(0));
+    aspeed_soc_uart_set_chr(s, uart_chosen, serial_hd(0));
     for (int i = 1, uart = ASPEED_DEV_UART1; i < sc->uarts_num; i++, uart++) {
-        if (uart == amc->uart_default) {
+        if (uart == uart_chosen) {
             continue;
         }
         aspeed_soc_uart_set_chr(s, uart, serial_hd(i));
@@ -1078,6 +1080,35 @@ static void aspeed_set_spi_model(Object *obj, const char *value, Error **errp)
     bmc->spi_model = g_strdup(value);
 }
 
+static char *aspeed_get_bmc_console(Object *obj, Error **errp)
+{
+    AspeedMachineState *bmc = ASPEED_MACHINE(obj);
+    AspeedMachineClass *amc = ASPEED_MACHINE_GET_CLASS(bmc);
+    int uart_chosen = bmc->uart_chosen ? bmc->uart_chosen : amc->uart_default;
+
+    return g_strdup_printf("uart%d", uart_chosen - ASPEED_DEV_UART1 + 1);
+}
+
+static void aspeed_set_bmc_console(Object *obj, const char *value, Error **errp)
+{
+    AspeedMachineState *bmc = ASPEED_MACHINE(obj);
+    AspeedMachineClass *amc = ASPEED_MACHINE_GET_CLASS(bmc);
+    AspeedSoCClass *sc = ASPEED_SOC_CLASS(object_class_by_name(amc->soc_name));
+    int val;
+
+    if (sscanf(value, "uart%u", &val) != 1) {
+        error_setg(errp, "Bad value for \"uart\" property");
+        return;
+    }
+
+    /* The number of UART depends on the SoC */
+    if (val < 1 || val > sc->uarts_num) {
+        error_setg(errp, "\"uart\" should be in range [1 - %d]", sc->uarts_num);
+        return;
+    }
+    bmc->uart_chosen = ASPEED_DEV_UART1 + val - 1;
+}
+
 static void aspeed_machine_class_props_init(ObjectClass *oc)
 {
     object_class_property_add_bool(oc, "execute-in-place",
@@ -1086,6 +1117,11 @@ static void aspeed_machine_class_props_init(ObjectClass *oc)
     object_class_property_set_description(oc, "execute-in-place",
                            "boot directly from CE0 flash device");
 
+    object_class_property_add_str(oc, "bmc-console", aspeed_get_bmc_console,
+                                  aspeed_set_bmc_console);
+    object_class_property_set_description(oc, "bmc-console",
+                           "Change the default UART to \"uartX\"");
+
     object_class_property_add_str(oc, "fmc-model", aspeed_get_fmc_model,
                                    aspeed_set_fmc_model);
     object_class_property_set_description(oc, "fmc-model",