arm: Stub out NRF51 TWI magnetometer/accelerometer detection

Recent microbit firmwares panic if the TWI magnetometer/accelerometer
devices are not detected during startup.  We don't implement TWI (I2C)
so let's stub out these devices just to let the firmware boot.

Signed-off by: Steffen Görtz <contrib@steffen-goertz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190110094020.18354-2-stefanha@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: fixed comment style]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 128 insertions, 0 deletions

diff --git a/hw/i2c/Makefile.objs b/hw/i2c/Makefile.objs
index 37cacde..82e747e 100644
--- a/hw/i2c/Makefile.objs
+++ b/hw/i2c/Makefile.objs
@@ -7,5 +7,6 @@ common-obj-$(CONFIG_BITBANG_I2C) += bitbang_i2c.o
 common-obj-$(CONFIG_EXYNOS4) += exynos4210_i2c.o
 common-obj-$(CONFIG_IMX_I2C) += imx_i2c.o
 common-obj-$(CONFIG_ASPEED_SOC) += aspeed_i2c.o
+common-obj-$(CONFIG_NRF51_SOC) += microbit_i2c.o
 obj-$(CONFIG_OMAP) += omap_i2c.o
 obj-$(CONFIG_PPC4XX) += ppc4xx_i2c.o
diff --git a/hw/i2c/microbit_i2c.c b/hw/i2c/microbit_i2c.c
new file mode 100644
index 0000000..793f1b0
--- /dev/null
+++ b/hw/i2c/microbit_i2c.c
@@ -0,0 +1,127 @@
+/*
+ * Microbit stub for Nordic Semiconductor nRF51 SoC Two-Wire Interface
+ * http://infocenter.nordicsemi.com/pdf/nRF51_RM_v3.0.1.pdf
+ *
+ * This is a microbit-specific stub for the TWI controller on the nRF51 SoC.
+ * We don't emulate I2C devices but the firmware probes the
+ * accelerometer/magnetometer on startup and panics if they are not found.
+ * Therefore we stub out the probing.
+ *
+ * In the future this file could evolve into a full nRF51 TWI controller
+ * device.
+ *
+ * Copyright 2018 Steffen Görtz <contrib@steffen-goertz.de>
+ * Copyright 2019 Red Hat, Inc.
+ *
+ * This code is licensed under the GPL version 2 or later.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "hw/i2c/microbit_i2c.h"
+
+static const uint32_t twi_read_sequence[] = {0x5A, 0x5A, 0x40};
+
+static uint64_t microbit_i2c_read(void *opaque, hwaddr addr, unsigned int size)
+{
+    MicrobitI2CState *s = opaque;
+    uint64_t data = 0x00;
+
+    switch (addr) {
+    case NRF51_TWI_EVENT_STOPPED:
+        data = 0x01;
+        break;
+    case NRF51_TWI_EVENT_RXDREADY:
+        data = 0x01;
+        break;
+    case NRF51_TWI_EVENT_TXDSENT:
+        data = 0x01;
+        break;
+    case NRF51_TWI_REG_RXD:
+        data = twi_read_sequence[s->read_idx];
+        if (s->read_idx < G_N_ELEMENTS(twi_read_sequence)) {
+            s->read_idx++;
+        }
+        break;
+    default:
+        data = s->regs[addr / sizeof(s->regs[0])];
+        break;
+    }
+
+    qemu_log_mask(LOG_UNIMP, "%s: 0x%" HWADDR_PRIx " [%u] = %" PRIx32 "\n",
+                  __func__, addr, size, (uint32_t)data);
+
+
+    return data;
+}
+
+static void microbit_i2c_write(void *opaque, hwaddr addr, uint64_t data,
+                               unsigned int size)
+{
+    MicrobitI2CState *s = opaque;
+
+    qemu_log_mask(LOG_UNIMP, "%s: 0x%" HWADDR_PRIx " <- 0x%" PRIx64 " [%u]\n",
+                  __func__, addr, data, size);
+    s->regs[addr / sizeof(s->regs[0])] = data;
+}
+
+static const MemoryRegionOps microbit_i2c_ops = {
+    .read = microbit_i2c_read,
+    .write = microbit_i2c_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .impl.min_access_size = 4,
+    .impl.max_access_size = 4,
+};
+
+static const VMStateDescription microbit_i2c_vmstate = {
+    .name = TYPE_MICROBIT_I2C,
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32_ARRAY(regs, MicrobitI2CState, MICROBIT_I2C_NREGS),
+        VMSTATE_UINT32(read_idx, MicrobitI2CState),
+    },
+};
+
+static void microbit_i2c_reset(DeviceState *dev)
+{
+    MicrobitI2CState *s = MICROBIT_I2C(dev);
+
+    memset(s->regs, 0, sizeof(s->regs));
+    s->read_idx = 0;
+}
+
+static void microbit_i2c_realize(DeviceState *dev, Error **errp)
+{
+    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
+    MicrobitI2CState *s = MICROBIT_I2C(dev);
+
+    memory_region_init_io(&s->iomem, OBJECT(s), &microbit_i2c_ops, s,
+                          "microbit.twi", NRF51_TWI_SIZE);
+    sysbus_init_mmio(sbd, &s->iomem);
+}
+
+static void microbit_i2c_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->vmsd = &microbit_i2c_vmstate;
+    dc->reset = microbit_i2c_reset;
+    dc->realize = microbit_i2c_realize;
+    dc->desc = "Microbit I2C controller";
+}
+
+static const TypeInfo microbit_i2c_info = {
+    .name = TYPE_MICROBIT_I2C,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(MicrobitI2CState),
+    .class_init = microbit_i2c_class_init,
+};
+
+static void microbit_i2c_register_types(void)
+{
+    type_register_static(&microbit_i2c_info);
+}
+
+type_init(microbit_i2c_register_types)