hw/arm/ast27x0: Add SRAM link and alias mapping for SSP coprocessor

AST2700 has a 128KB SRAM, physically mapped at 0x10000000–0x1001FFFF for
the PSP (CA35) processor. The SSP coprocessor shares this same SRAM but
accesses it through a different address window at 0x70000000–0x7001FFFF.

To model this shared-memory behavior in QEMU, this commit introduces a
linked SRAM property and alias mapping between the PSP and SSP subsystems.

Changes include:
- Add a "MemoryRegion *sram" link and "MemoryRegion sram_alias" to
  AspeedCoprocessorState.
- Register the new "sram" property in aspeed_coprocessor_common.c.
- In aspeed_ast27x0-fc.c, connect the SSP coprocessor’s "sram" link to
  the PSP’s SRAM region.
- In aspeed_ast27x0-ssp.c, create an alias mapping for SRAM at
  0x70000000 – 0x7001FFFF in the SSP’s memory map.

This ensures that the SSP can correctly access the shared SRAM contents
through its own address space while maintaining a consistent physical
backing region. It also guarantees that the SRAM is realized before the
SSP device, ensuring successful alias setup.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20251015062210.3128710-4-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/arm/aspeed_ast27x0-fc.c

@@ -118,6 +118,8 @@ static bool ast2700fc_ssp_init(MachineState *machine, Error **errp)
     AspeedCoprocessorState *soc;
     AspeedCoprocessorClass *sc;
     Ast2700FCState *s = AST2700A1FC(machine);
+    AspeedSoCState *psp = ASPEED_SOC(&s->ca35);
+
     s->ssp_sysclk = clock_new(OBJECT(s), "SSP_SYSCLK");
     clock_set_hz(s->ssp_sysclk, 200000000ULL);
 
@@ -134,6 +136,8 @@ static bool ast2700fc_ssp_init(MachineState *machine, Error **errp)
     sc = ASPEED_COPROCESSOR_GET_CLASS(soc);
     aspeed_soc_uart_set_chr(soc->uart, ASPEED_DEV_UART4, sc->uarts_base,
                             sc->uarts_num, serial_hd(1));
+    object_property_set_link(OBJECT(&s->ssp), "sram",
+                             OBJECT(&psp->sram), &error_abort);
     if (!qdev_realize(DEVICE(&s->ssp), NULL, errp)) {
         return false;
     }

hw/arm/aspeed_ast27x0-ssp.c

@@ -20,6 +20,7 @@
 
 static const hwaddr aspeed_soc_ast27x0ssp_memmap[] = {
     [ASPEED_DEV_SDRAM]     =  0x00000000,
+    [ASPEED_DEV_SRAM]      =  0x70000000,
     [ASPEED_DEV_INTC]      =  0x72100000,
     [ASPEED_DEV_SCU]       =  0x72C02000,
     [ASPEED_DEV_SCUIO]     =  0x74C02000,
@@ -195,6 +196,12 @@ static void aspeed_soc_ast27x0ssp_realize(DeviceState *dev_soc, Error **errp)
                                 sc->memmap[ASPEED_DEV_SDRAM],
                                 &s->sdram);
 
+    /* SRAM */
+    memory_region_init_alias(&s->sram_alias, OBJECT(s), "sram.alias",
+                             s->sram, 0, memory_region_size(s->sram));
+    memory_region_add_subregion(s->memory, sc->memmap[ASPEED_DEV_SRAM],
+                                &s->sram_alias);
+
     /* SCU */
     if (!sysbus_realize(SYS_BUS_DEVICE(&s->scu), errp)) {
         return;

hw/arm/aspeed_coprocessor_common.c

@@ -25,6 +25,8 @@ static void aspeed_coprocessor_realize(DeviceState *dev, Error **errp)
 static const Property aspeed_coprocessor_properties[] = {
     DEFINE_PROP_LINK("memory", AspeedCoprocessorState, memory,
                      TYPE_MEMORY_REGION, MemoryRegion *),
+    DEFINE_PROP_LINK("sram", AspeedCoprocessorState, sram, TYPE_MEMORY_REGION,
+                     MemoryRegion *),
 };
 
 static void aspeed_coprocessor_class_init(ObjectClass *oc, const void *data)

include/hw/arm/aspeed_coprocessor.h

@@ -17,7 +17,8 @@ struct AspeedCoprocessorState {
 
     MemoryRegion *memory;
     MemoryRegion sdram;
-    MemoryRegion sram;
+    MemoryRegion *sram;
+    MemoryRegion sram_alias;
     Clock *sysclk;
 
     AspeedSCUState scu;