hw/char/cmsdk-apb-uart.c: Implement CMSDK APB UART

Implement a model of the simple "APB UART" provided in
the Cortex-M System Design Kit (CMSDK).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1500029487-14822-3-git-send-email-peter.maydell@linaro.org
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

3 files changed, 413 insertions, 0 deletions

diff --git a/hw/char/Makefile.objs b/hw/char/Makefile.objs
index 55fcb68fd2..1bcd37e98d 100644
--- a/hw/char/Makefile.objs
+++ b/hw/char/Makefile.objs
@@ -19,6 +19,7 @@ obj-$(CONFIG_DIGIC) += digic-uart.o
 obj-$(CONFIG_STM32F2XX_USART) += stm32f2xx_usart.o
 obj-$(CONFIG_RASPI) += bcm2835_aux.o
 
+common-obj-$(CONFIG_CMSDK_APB_UART) += cmsdk-apb-uart.o
 common-obj-$(CONFIG_ETRAXFS) += etraxfs_ser.o
 common-obj-$(CONFIG_ISA_DEBUG) += debugcon.o
 common-obj-$(CONFIG_GRLIB) += grlib_apbuart.o
diff --git a/hw/char/cmsdk-apb-uart.c b/hw/char/cmsdk-apb-uart.c
new file mode 100644
index 0000000000..ab34729cb2
--- /dev/null
+++ b/hw/char/cmsdk-apb-uart.c
@@ -0,0 +1,403 @@
+/*
+ * ARM CMSDK APB UART emulation
+ *
+ * Copyright (c) 2017 Linaro Limited
+ * Written by Peter Maydell
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 or
+ *  (at your option) any later version.
+ */
+
+/* This is a model of the "APB UART" which is part of the Cortex-M
+ * System Design Kit (CMSDK) and documented in the Cortex-M System
+ * Design Kit Technical Reference Manual (ARM DDI0479C):
+ * https://developer.arm.com/products/system-design/system-design-kits/cortex-m-system-design-kit
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "qapi/error.h"
+#include "trace.h"
+#include "hw/sysbus.h"
+#include "hw/registerfields.h"
+#include "chardev/char-fe.h"
+#include "chardev/char-serial.h"
+#include "hw/char/cmsdk-apb-uart.h"
+
+REG32(DATA, 0)
+REG32(STATE, 4)
+    FIELD(STATE, TXFULL, 0, 1)
+    FIELD(STATE, RXFULL, 1, 1)
+    FIELD(STATE, TXOVERRUN, 2, 1)
+    FIELD(STATE, RXOVERRUN, 3, 1)
+REG32(CTRL, 8)
+    FIELD(CTRL, TX_EN, 0, 1)
+    FIELD(CTRL, RX_EN, 1, 1)
+    FIELD(CTRL, TX_INTEN, 2, 1)
+    FIELD(CTRL, RX_INTEN, 3, 1)
+    FIELD(CTRL, TXO_INTEN, 4, 1)
+    FIELD(CTRL, RXO_INTEN, 5, 1)
+    FIELD(CTRL, HSTEST, 6, 1)
+REG32(INTSTATUS, 0xc)
+    FIELD(INTSTATUS, TX, 0, 1)
+    FIELD(INTSTATUS, RX, 1, 1)
+    FIELD(INTSTATUS, TXO, 2, 1)
+    FIELD(INTSTATUS, RXO, 3, 1)
+REG32(BAUDDIV, 0x10)
+REG32(PID4, 0xFD0)
+REG32(PID5, 0xFD4)
+REG32(PID6, 0xFD8)
+REG32(PID7, 0xFDC)
+REG32(PID0, 0xFE0)
+REG32(PID1, 0xFE4)
+REG32(PID2, 0xFE8)
+REG32(PID3, 0xFEC)
+REG32(CID0, 0xFF0)
+REG32(CID1, 0xFF4)
+REG32(CID2, 0xFF8)
+REG32(CID3, 0xFFC)
+
+/* PID/CID values */
+static const int uart_id[] = {
+    0x04, 0x00, 0x00, 0x00, /* PID4..PID7 */
+    0x21, 0xb8, 0x1b, 0x00, /* PID0..PID3 */
+    0x0d, 0xf0, 0x05, 0xb1, /* CID0..CID3 */
+};
+
+static bool uart_baudrate_ok(CMSDKAPBUART *s)
+{
+    /* The minimum permitted bauddiv setting is 16, so we just ignore
+     * settings below that (usually this means the device has just
+     * been reset and not yet programmed).
+     */
+    return s->bauddiv >= 16 && s->bauddiv <= s->pclk_frq;
+}
+
+static void uart_update_parameters(CMSDKAPBUART *s)
+{
+    QEMUSerialSetParams ssp;
+
+    /* This UART is always 8N1 but the baud rate is programmable. */
+    if (!uart_baudrate_ok(s)) {
+        return;
+    }
+
+    ssp.data_bits = 8;
+    ssp.parity = 'N';
+    ssp.stop_bits = 1;
+    ssp.speed = s->pclk_frq / s->bauddiv;
+    qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
+    trace_cmsdk_apb_uart_set_params(ssp.speed);
+}
+
+static void cmsdk_apb_uart_update(CMSDKAPBUART *s)
+{
+    /* update outbound irqs, including handling the way the rxo and txo
+     * interrupt status bits are just logical AND of the overrun bit in
+     * STATE and the overrun interrupt enable bit in CTRL.
+     */
+    uint32_t omask = (R_INTSTATUS_RXO_MASK | R_INTSTATUS_TXO_MASK);
+    s->intstatus &= ~omask;
+    s->intstatus |= (s->state & (s->ctrl >> 2) & omask);
+
+    qemu_set_irq(s->txint, !!(s->intstatus & R_INTSTATUS_TX_MASK));
+    qemu_set_irq(s->rxint, !!(s->intstatus & R_INTSTATUS_RX_MASK));
+    qemu_set_irq(s->txovrint, !!(s->intstatus & R_INTSTATUS_TXO_MASK));
+    qemu_set_irq(s->rxovrint, !!(s->intstatus & R_INTSTATUS_RXO_MASK));
+    qemu_set_irq(s->uartint, !!(s->intstatus));
+}
+
+static int uart_can_receive(void *opaque)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+
+    /* We can take a char if RX is enabled and the buffer is empty */
+    if (s->ctrl & R_CTRL_RX_EN_MASK && !(s->state & R_STATE_RXFULL_MASK)) {
+        return 1;
+    }
+    return 0;
+}
+
+static void uart_receive(void *opaque, const uint8_t *buf, int size)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+
+    trace_cmsdk_apb_uart_receive(*buf);
+
+    /* In fact uart_can_receive() ensures that we can't be
+     * called unless RX is enabled and the buffer is empty,
+     * but we include this logic as documentation of what the
+     * hardware does if a character arrives in these circumstances.
+     */
+    if (!(s->ctrl & R_CTRL_RX_EN_MASK)) {
+        /* Just drop the character on the floor */
+        return;
+    }
+
+    if (s->state & R_STATE_RXFULL_MASK) {
+        s->state |= R_STATE_RXOVERRUN_MASK;
+    }
+
+    s->rxbuf = *buf;
+    s->state |= R_STATE_RXFULL_MASK;
+    if (s->ctrl & R_CTRL_RX_INTEN_MASK) {
+        s->intstatus |= R_INTSTATUS_RX_MASK;
+    }
+    cmsdk_apb_uart_update(s);
+}
+
+static uint64_t uart_read(void *opaque, hwaddr offset, unsigned size)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+    uint64_t r;
+
+    switch (offset) {
+    case A_DATA:
+        r = s->rxbuf;
+        s->state &= ~R_STATE_RXFULL_MASK;
+        cmsdk_apb_uart_update(s);
+        break;
+    case A_STATE:
+        r = s->state;
+        break;
+    case A_CTRL:
+        r = s->ctrl;
+        break;
+    case A_INTSTATUS:
+        r = s->intstatus;
+        break;
+    case A_BAUDDIV:
+        r = s->bauddiv;
+        break;
+    case A_PID4 ... A_CID3:
+        r = uart_id[(offset - A_PID4) / 4];
+        break;
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "CMSDK APB UART read: bad offset %x\n", (int) offset);
+        r = 0;
+        break;
+    }
+    trace_cmsdk_apb_uart_read(offset, r, size);
+    return r;
+}
+
+/* Try to send tx data, and arrange to be called back later if
+ * we can't (ie the char backend is busy/blocking).
+ */
+static gboolean uart_transmit(GIOChannel *chan, GIOCondition cond, void *opaque)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+    int ret;
+
+    s->watch_tag = 0;
+
+    if (!(s->ctrl & R_CTRL_TX_EN_MASK) || !(s->state & R_STATE_TXFULL_MASK)) {
+        return FALSE;
+    }
+
+    ret = qemu_chr_fe_write(&s->chr, &s->txbuf, 1);
+    if (ret <= 0) {
+        s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
+                                             uart_transmit, s);
+        if (!s->watch_tag) {
+            /* Most common reason to be here is "no chardev backend":
+             * just insta-drain the buffer, so the serial output
+             * goes into a void, rather than blocking the guest.
+             */
+            goto buffer_drained;
+        }
+        /* Transmit pending */
+        trace_cmsdk_apb_uart_tx_pending();
+        return FALSE;
+    }
+
+buffer_drained:
+    /* Character successfully sent */
+    trace_cmsdk_apb_uart_tx(s->txbuf);
+    s->state &= ~R_STATE_TXFULL_MASK;
+    /* Going from TXFULL set to clear triggers the tx interrupt */
+    if (s->ctrl & R_CTRL_TX_INTEN_MASK) {
+        s->intstatus |= R_INTSTATUS_TX_MASK;
+    }
+    cmsdk_apb_uart_update(s);
+    return FALSE;
+}
+
+static void uart_cancel_transmit(CMSDKAPBUART *s)
+{
+    if (s->watch_tag) {
+        g_source_remove(s->watch_tag);
+        s->watch_tag = 0;
+    }
+}
+
+static void uart_write(void *opaque, hwaddr offset, uint64_t value,
+                       unsigned size)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+
+    trace_cmsdk_apb_uart_write(offset, value, size);
+
+    switch (offset) {
+    case A_DATA:
+        s->txbuf = value;
+        if (s->state & R_STATE_TXFULL_MASK) {
+            /* Buffer already full -- note the overrun and let the
+             * existing pending transmit callback handle the new char.
+             */
+            s->state |= R_STATE_TXOVERRUN_MASK;
+            cmsdk_apb_uart_update(s);
+        } else {
+            s->state |= R_STATE_TXFULL_MASK;
+            uart_transmit(NULL, G_IO_OUT, s);
+        }
+        break;
+    case A_STATE:
+        /* Bits 0 and 1 are read only; bits 2 and 3 are W1C */
+        s->state &= ~(value &
+                      (R_STATE_TXOVERRUN_MASK | R_STATE_RXOVERRUN_MASK));
+        cmsdk_apb_uart_update(s);
+        break;
+    case A_CTRL:
+        s->ctrl = value & 0x7f;
+        if ((s->ctrl & R_CTRL_TX_EN_MASK) && !uart_baudrate_ok(s)) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "CMSDK APB UART: Tx enabled with invalid baudrate\n");
+        }
+        cmsdk_apb_uart_update(s);
+        break;
+    case A_INTSTATUS:
+        /* All bits are W1C. Clearing the overrun interrupt bits really
+         * clears the overrun status bits in the STATE register (which
+         * is then reflected into the intstatus value by the update function).
+         */
+        s->state &= ~(value & (R_INTSTATUS_TXO_MASK | R_INTSTATUS_RXO_MASK));
+        cmsdk_apb_uart_update(s);
+        break;
+    case A_BAUDDIV:
+        s->bauddiv = value & 0xFFFFF;
+        uart_update_parameters(s);
+        break;
+    case A_PID4 ... A_CID3:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "CMSDK APB UART write: write to RO offset 0x%x\n",
+                      (int)offset);
+        break;
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "CMSDK APB UART write: bad offset 0x%x\n", (int) offset);
+        break;
+    }
+}
+
+static const MemoryRegionOps uart_ops = {
+    .read = uart_read,
+    .write = uart_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
+static void cmsdk_apb_uart_reset(DeviceState *dev)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(dev);
+
+    trace_cmsdk_apb_uart_reset();
+    uart_cancel_transmit(s);
+    s->state = 0;
+    s->ctrl = 0;
+    s->intstatus = 0;
+    s->bauddiv = 0;
+    s->txbuf = 0;
+    s->rxbuf = 0;
+}
+
+static void cmsdk_apb_uart_init(Object *obj)
+{
+    SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
+    CMSDKAPBUART *s = CMSDK_APB_UART(obj);
+
+    memory_region_init_io(&s->iomem, obj, &uart_ops, s, "uart", 0x1000);
+    sysbus_init_mmio(sbd, &s->iomem);
+    sysbus_init_irq(sbd, &s->txint);
+    sysbus_init_irq(sbd, &s->rxint);
+    sysbus_init_irq(sbd, &s->txovrint);
+    sysbus_init_irq(sbd, &s->rxovrint);
+    sysbus_init_irq(sbd, &s->uartint);
+}
+
+static void cmsdk_apb_uart_realize(DeviceState *dev, Error **errp)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(dev);
+
+    if (s->pclk_frq == 0) {
+        error_setg(errp, "CMSDK APB UART: pclk-frq property must be set");
+        return;
+    }
+
+    /* This UART has no flow control, so we do not need to register
+     * an event handler to deal with CHR_EVENT_BREAK.
+     */
+    qemu_chr_fe_set_handlers(&s->chr, uart_can_receive, uart_receive,
+                             NULL, s, NULL, true);
+}
+
+static int cmsdk_apb_uart_post_load(void *opaque, int version_id)
+{
+    CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
+
+    /* If we have a pending character, arrange to resend it. */
+    if (s->state & R_STATE_TXFULL_MASK) {
+        s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
+                                             uart_transmit, s);
+    }
+    uart_update_parameters(s);
+    return 0;
+}
+
+static const VMStateDescription cmsdk_apb_uart_vmstate = {
+    .name = "cmsdk-apb-uart",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = cmsdk_apb_uart_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(state, CMSDKAPBUART),
+        VMSTATE_UINT32(ctrl, CMSDKAPBUART),
+        VMSTATE_UINT32(intstatus, CMSDKAPBUART),
+        VMSTATE_UINT32(bauddiv, CMSDKAPBUART),
+        VMSTATE_UINT8(txbuf, CMSDKAPBUART),
+        VMSTATE_UINT8(rxbuf, CMSDKAPBUART),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static Property cmsdk_apb_uart_properties[] = {
+    DEFINE_PROP_CHR("chardev", CMSDKAPBUART, chr),
+    DEFINE_PROP_UINT32("pclk-frq", CMSDKAPBUART, pclk_frq, 0),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void cmsdk_apb_uart_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->realize = cmsdk_apb_uart_realize;
+    dc->vmsd = &cmsdk_apb_uart_vmstate;
+    dc->reset = cmsdk_apb_uart_reset;
+    dc->props = cmsdk_apb_uart_properties;
+}
+
+static const TypeInfo cmsdk_apb_uart_info = {
+    .name = TYPE_CMSDK_APB_UART,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(CMSDKAPBUART),
+    .instance_init = cmsdk_apb_uart_init,
+    .class_init = cmsdk_apb_uart_class_init,
+};
+
+static void cmsdk_apb_uart_register_types(void)
+{
+    type_register_static(&cmsdk_apb_uart_info);
+}
+
+type_init(cmsdk_apb_uart_register_types);
diff --git a/hw/char/trace-events b/hw/char/trace-events
index 7fd48bb80d..daf4ee470a 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -56,3 +56,12 @@ pl011_write(uint32_t addr, uint32_t value) "addr 0x%08x value 0x%08x"
 pl011_can_receive(uint32_t lcr, int read_count, int r) "LCR %08x read_count %d returning %d"
 pl011_put_fifo(uint32_t c, int read_count) "new char 0x%x read_count now %d"
 pl011_put_fifo_full(void) "FIFO now full, RXFF set"
+
+# hw/char/cmsdk_apb_uart.c
+cmsdk_apb_uart_read(uint64_t offset, uint64_t data, unsigned size) "CMSDK APB UART read: offset 0x%" PRIx64 " data 0x%" PRIx64 " size %u"
+cmsdk_apb_uart_write(uint64_t offset, uint64_t data, unsigned size) "CMSDK APB UART write: offset 0x%" PRIx64 " data 0x%" PRIx64 " size %u"
+cmsdk_apb_uart_reset(void) "CMSDK APB UART: reset"
+cmsdk_apb_uart_receive(uint8_t c) "CMSDK APB UART: got character 0x%x from backend"
+cmsdk_apb_uart_tx_pending(void) "CMSDK APB UART: character send to backend pending"
+cmsdk_apb_uart_tx(uint8_t c) "CMSDK APB UART: character 0x%x sent to backend"
+cmsdk_apb_uart_set_params(int speed) "CMSDK APB UART: params set to %d 8N1"