hw/intc/armv7m_nvic: Implement read/write for RAS register block

The RAS feature has a block of memory-mapped registers at offset
0x5000 within the PPB.  For a "minimal RAS" implementation we provide
no error records and so the only registers that exist in the block
are ERRIIDR and ERRDEVID.

The "RAZ/WI for privileged, BusFault for nonprivileged" behaviour
of the "nvic-default" region is actually valid for minimal-RAS,
so the main benefit of providing an explicit implementation of
the register block is more accurate LOG_UNIMP messages, and a
framework for where we could add a real RAS implementation later
if necessary.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-27-peter.maydell@linaro.org

hw/intc/armv7m_nvic.c

@@ -2519,6 +2519,56 @@ static const MemoryRegionOps nvic_systick_ops = {
     .endianness = DEVICE_NATIVE_ENDIAN,
 };
 
+
+static MemTxResult ras_read(void *opaque, hwaddr addr,
+                            uint64_t *data, unsigned size,
+                            MemTxAttrs attrs)
+{
+    if (attrs.user) {
+        return MEMTX_ERROR;
+    }
+
+    switch (addr) {
+    case 0xe10: /* ERRIIDR */
+        /* architect field = Arm; product/variant/revision 0 */
+        *data = 0x43b;
+        break;
+    case 0xfc8: /* ERRDEVID */
+        /* Minimal RAS: we implement 0 error record indexes */
+        *data = 0;
+        break;
+    default:
+        qemu_log_mask(LOG_UNIMP, "Read RAS register offset 0x%x\n",
+                      (uint32_t)addr);
+        *data = 0;
+        break;
+    }
+    return MEMTX_OK;
+}
+
+static MemTxResult ras_write(void *opaque, hwaddr addr,
+                             uint64_t value, unsigned size,
+                             MemTxAttrs attrs)
+{
+    if (attrs.user) {
+        return MEMTX_ERROR;
+    }
+
+    switch (addr) {
+    default:
+        qemu_log_mask(LOG_UNIMP, "Write to RAS register offset 0x%x\n",
+                      (uint32_t)addr);
+        break;
+    }
+    return MEMTX_OK;
+}
+
+static const MemoryRegionOps ras_ops = {
+    .read_with_attrs = ras_read,
+    .write_with_attrs = ras_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
 /*
  * Unassigned portions of the PPB space are RAZ/WI for privileged
  * accesses, and fault for non-privileged accesses.
@@ -2866,6 +2916,12 @@ static void armv7m_nvic_realize(DeviceState *dev, Error **errp)
                                             &s->systick_ns_mem, 1);
     }
 
+    if (cpu_isar_feature(aa32_ras, s->cpu)) {
+        memory_region_init_io(&s->ras_mem, OBJECT(s),
+                              &ras_ops, s, "nvic_ras", 0x1000);
+        memory_region_add_subregion(&s->container, 0x5000, &s->ras_mem);
+    }
+
     sysbus_init_mmio(SYS_BUS_DEVICE(dev), &s->container);
 }
 

include/hw/intc/armv7m_nvic.h

@@ -83,6 +83,7 @@ struct NVICState {
     MemoryRegion sysreg_ns_mem;
     MemoryRegion systickmem;
     MemoryRegion systick_ns_mem;
+    MemoryRegion ras_mem;
     MemoryRegion container;
     MemoryRegion defaultmem;