hw/char/cmsdk-apb-uart.c

   1 /*
   2  * ARM CMSDK APB UART emulation
   3  *
   4  * Copyright (c) 2017 Linaro Limited
   5  * Written by Peter Maydell
   6  *
   7  *  This program is free software; you can redistribute it and/or modify
   8  *  it under the terms of the GNU General Public License version 2 or
   9  *  (at your option) any later version.
  10  */
  11
  12 /* This is a model of the "APB UART" which is part of the Cortex-M
  13  * System Design Kit (CMSDK) and documented in the Cortex-M System
  14  * Design Kit Technical Reference Manual (ARM DDI0479C):
  15  * https://developer.arm.com/products/system-design/system-design-kits/cortex-m-system-design-kit
  16  */
  17
  18 #include "qemu/osdep.h"
  19 #include "qemu/log.h"
  20 #include "qemu/module.h"
  21 #include "qapi/error.h"
  22 #include "trace.h"
  23 #include "hw/sysbus.h"
  24 #include "migration/vmstate.h"
  25 #include "hw/registerfields.h"
  26 #include "chardev/char-fe.h"
  27 #include "chardev/char-serial.h"
  28 #include "hw/char/cmsdk-apb-uart.h"
  29 #include "hw/irq.h"
  30 #include "hw/qdev-properties-system.h"
  31
  32 REG32(DATA, 0)
  33 REG32(STATE, 4)
  34     FIELD(STATE, TXFULL, 0, 1)
  35     FIELD(STATE, RXFULL, 1, 1)
  36     FIELD(STATE, TXOVERRUN, 2, 1)
  37     FIELD(STATE, RXOVERRUN, 3, 1)
  38 REG32(CTRL, 8)
  39     FIELD(CTRL, TX_EN, 0, 1)
  40     FIELD(CTRL, RX_EN, 1, 1)
  41     FIELD(CTRL, TX_INTEN, 2, 1)
  42     FIELD(CTRL, RX_INTEN, 3, 1)
  43     FIELD(CTRL, TXO_INTEN, 4, 1)
  44     FIELD(CTRL, RXO_INTEN, 5, 1)
  45     FIELD(CTRL, HSTEST, 6, 1)
  46 REG32(INTSTATUS, 0xc)
  47     FIELD(INTSTATUS, TX, 0, 1)
  48     FIELD(INTSTATUS, RX, 1, 1)
  49     FIELD(INTSTATUS, TXO, 2, 1)
  50     FIELD(INTSTATUS, RXO, 3, 1)
  51 REG32(BAUDDIV, 0x10)
  52 REG32(PID4, 0xFD0)
  53 REG32(PID5, 0xFD4)
  54 REG32(PID6, 0xFD8)
  55 REG32(PID7, 0xFDC)
  56 REG32(PID0, 0xFE0)
  57 REG32(PID1, 0xFE4)
  58 REG32(PID2, 0xFE8)
  59 REG32(PID3, 0xFEC)
  60 REG32(CID0, 0xFF0)
  61 REG32(CID1, 0xFF4)
  62 REG32(CID2, 0xFF8)
  63 REG32(CID3, 0xFFC)
  64
  65 /* PID/CID values */
  66 static const int uart_id[] = {
  67     0x04, 0x00, 0x00, 0x00, /* PID4..PID7 */
  68     0x21, 0xb8, 0x1b, 0x00, /* PID0..PID3 */
  69     0x0d, 0xf0, 0x05, 0xb1, /* CID0..CID3 */
  70 };
  71
  72 static bool uart_baudrate_ok(CMSDKAPBUART *s)
  73 {
  74     /* The minimum permitted bauddiv setting is 16, so we just ignore
  75      * settings below that (usually this means the device has just
  76      * been reset and not yet programmed).
  77      */
  78     return s->bauddiv >= 16 && s->bauddiv <= s->pclk_frq;
  79 }
  80
  81 static void uart_update_parameters(CMSDKAPBUART *s)
  82 {
  83     QEMUSerialSetParams ssp;
  84
  85     /* This UART is always 8N1 but the baud rate is programmable. */
  86     if (!uart_baudrate_ok(s)) {
  87         return;
  88     }
  89
  90     ssp.data_bits = 8;
  91     ssp.parity = 'N';
  92     ssp.stop_bits = 1;
  93     ssp.speed = s->pclk_frq / s->bauddiv;
  94     qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
  95     trace_cmsdk_apb_uart_set_params(ssp.speed);
  96 }
  97
  98 static void cmsdk_apb_uart_update(CMSDKAPBUART *s)
  99 {
 100     /* update outbound irqs, including handling the way the rxo and txo
 101      * interrupt status bits are just logical AND of the overrun bit in
 102      * STATE and the overrun interrupt enable bit in CTRL.
 103      */
 104     uint32_t omask = (R_INTSTATUS_RXO_MASK | R_INTSTATUS_TXO_MASK);
 105     s->intstatus &= ~omask;
 106     s->intstatus |= (s->state & (s->ctrl >> 2) & omask);
 107
 108     qemu_set_irq(s->txint, !!(s->intstatus & R_INTSTATUS_TX_MASK));
 109     qemu_set_irq(s->rxint, !!(s->intstatus & R_INTSTATUS_RX_MASK));
 110     qemu_set_irq(s->txovrint, !!(s->intstatus & R_INTSTATUS_TXO_MASK));
 111     qemu_set_irq(s->rxovrint, !!(s->intstatus & R_INTSTATUS_RXO_MASK));
 112     qemu_set_irq(s->uartint, !!(s->intstatus));
 113 }
 114
 115 static int uart_can_receive(void *opaque)
 116 {
 117     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 118
 119     /* We can take a char if RX is enabled and the buffer is empty */
 120     if (s->ctrl & R_CTRL_RX_EN_MASK && !(s->state & R_STATE_RXFULL_MASK)) {
 121         return 1;
 122     }
 123     return 0;
 124 }
 125
 126 static void uart_receive(void *opaque, const uint8_t *buf, int size)
 127 {
 128     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 129
 130     trace_cmsdk_apb_uart_receive(*buf);
 131
 132     /* In fact uart_can_receive() ensures that we can't be
 133      * called unless RX is enabled and the buffer is empty,
 134      * but we include this logic as documentation of what the
 135      * hardware does if a character arrives in these circumstances.
 136      */
 137     if (!(s->ctrl & R_CTRL_RX_EN_MASK)) {
 138         /* Just drop the character on the floor */
 139         return;
 140     }
 141
 142     if (s->state & R_STATE_RXFULL_MASK) {
 143         s->state |= R_STATE_RXOVERRUN_MASK;
 144     }
 145
 146     s->rxbuf = *buf;
 147     s->state |= R_STATE_RXFULL_MASK;
 148     if (s->ctrl & R_CTRL_RX_INTEN_MASK) {
 149         s->intstatus |= R_INTSTATUS_RX_MASK;
 150     }
 151     cmsdk_apb_uart_update(s);
 152 }
 153
 154 static uint64_t uart_read(void *opaque, hwaddr offset, unsigned size)
 155 {
 156     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 157     uint64_t r;
 158
 159     switch (offset) {
 160     case A_DATA:
 161         r = s->rxbuf;
 162         s->state &= ~R_STATE_RXFULL_MASK;
 163         cmsdk_apb_uart_update(s);
 164         qemu_chr_fe_accept_input(&s->chr);
 165         break;
 166     case A_STATE:
 167         r = s->state;
 168         break;
 169     case A_CTRL:
 170         r = s->ctrl;
 171         break;
 172     case A_INTSTATUS:
 173         r = s->intstatus;
 174         break;
 175     case A_BAUDDIV:
 176         r = s->bauddiv;
 177         break;
 178     case A_PID4 ... A_CID3:
 179         r = uart_id[(offset - A_PID4) / 4];
 180         break;
 181     default:
 182         qemu_log_mask(LOG_GUEST_ERROR,
 183                       "CMSDK APB UART read: bad offset %x\n", (int) offset);
 184         r = 0;
 185         break;
 186     }
 187     trace_cmsdk_apb_uart_read(offset, r, size);
 188     return r;
 189 }
 190
 191 /* Try to send tx data, and arrange to be called back later if
 192  * we can't (ie the char backend is busy/blocking).
 193  */
 194 static gboolean uart_transmit(void *do_not_use, GIOCondition cond, void *opaque)
 195 {
 196     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 197     int ret;
 198
 199     s->watch_tag = 0;
 200
 201     if (!(s->ctrl & R_CTRL_TX_EN_MASK) || !(s->state & R_STATE_TXFULL_MASK)) {
 202         return G_SOURCE_REMOVE;
 203     }
 204
 205     ret = qemu_chr_fe_write(&s->chr, &s->txbuf, 1);
 206     if (ret <= 0) {
 207         s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
 208                                              uart_transmit, s);
 209         if (!s->watch_tag) {
 210             /* Most common reason to be here is "no chardev backend":
 211              * just insta-drain the buffer, so the serial output
 212              * goes into a void, rather than blocking the guest.
 213              */
 214             goto buffer_drained;
 215         }
 216         /* Transmit pending */
 217         trace_cmsdk_apb_uart_tx_pending();
 218         return G_SOURCE_REMOVE;
 219     }
 220
 221 buffer_drained:
 222     /* Character successfully sent */
 223     trace_cmsdk_apb_uart_tx(s->txbuf);
 224     s->state &= ~R_STATE_TXFULL_MASK;
 225     /* Going from TXFULL set to clear triggers the tx interrupt */
 226     if (s->ctrl & R_CTRL_TX_INTEN_MASK) {
 227         s->intstatus |= R_INTSTATUS_TX_MASK;
 228     }
 229     cmsdk_apb_uart_update(s);
 230     return G_SOURCE_REMOVE;
 231 }
 232
 233 static void uart_cancel_transmit(CMSDKAPBUART *s)
 234 {
 235     if (s->watch_tag) {
 236         g_source_remove(s->watch_tag);
 237         s->watch_tag = 0;
 238     }
 239 }
 240
 241 static void uart_write(void *opaque, hwaddr offset, uint64_t value,
 242                        unsigned size)
 243 {
 244     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 245
 246     trace_cmsdk_apb_uart_write(offset, value, size);
 247
 248     switch (offset) {
 249     case A_DATA:
 250         s->txbuf = value;
 251         if (s->state & R_STATE_TXFULL_MASK) {
 252             /* Buffer already full -- note the overrun and let the
 253              * existing pending transmit callback handle the new char.
 254              */
 255             s->state |= R_STATE_TXOVERRUN_MASK;
 256             cmsdk_apb_uart_update(s);
 257         } else {
 258             s->state |= R_STATE_TXFULL_MASK;
 259             uart_transmit(NULL, G_IO_OUT, s);
 260         }
 261         break;
 262     case A_STATE:
 263         /* Bits 0 and 1 are read only; bits 2 and 3 are W1C */
 264         s->state &= ~(value &
 265                       (R_STATE_TXOVERRUN_MASK | R_STATE_RXOVERRUN_MASK));
 266         cmsdk_apb_uart_update(s);
 267         break;
 268     case A_CTRL:
 269         s->ctrl = value & 0x7f;
 270         if ((s->ctrl & R_CTRL_TX_EN_MASK) && !uart_baudrate_ok(s)) {
 271             qemu_log_mask(LOG_GUEST_ERROR,
 272                           "CMSDK APB UART: Tx enabled with invalid baudrate\n");
 273         }
 274         cmsdk_apb_uart_update(s);
 275         break;
 276     case A_INTSTATUS:
 277         /* All bits are W1C. Clearing the overrun interrupt bits really
 278          * clears the overrun status bits in the STATE register (which
 279          * is then reflected into the intstatus value by the update function).
 280          */
 281         s->state &= ~(value & (R_INTSTATUS_TXO_MASK | R_INTSTATUS_RXO_MASK));
 282         s->intstatus &= ~value;
 283         cmsdk_apb_uart_update(s);
 284         break;
 285     case A_BAUDDIV:
 286         s->bauddiv = value & 0xFFFFF;
 287         uart_update_parameters(s);
 288         break;
 289     case A_PID4 ... A_CID3:
 290         qemu_log_mask(LOG_GUEST_ERROR,
 291                       "CMSDK APB UART write: write to RO offset 0x%x\n",
 292                       (int)offset);
 293         break;
 294     default:
 295         qemu_log_mask(LOG_GUEST_ERROR,
 296                       "CMSDK APB UART write: bad offset 0x%x\n", (int) offset);
 297         break;
 298     }
 299 }
 300
 301 static const MemoryRegionOps uart_ops = {
 302     .read = uart_read,
 303     .write = uart_write,
 304     .endianness = DEVICE_LITTLE_ENDIAN,
 305 };
 306
 307 static void cmsdk_apb_uart_reset(DeviceState *dev)
 308 {
 309     CMSDKAPBUART *s = CMSDK_APB_UART(dev);
 310
 311     trace_cmsdk_apb_uart_reset();
 312     uart_cancel_transmit(s);
 313     s->state = 0;
 314     s->ctrl = 0;
 315     s->intstatus = 0;
 316     s->bauddiv = 0;
 317     s->txbuf = 0;
 318     s->rxbuf = 0;
 319 }
 320
 321 static void cmsdk_apb_uart_init(Object *obj)
 322 {
 323     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
 324     CMSDKAPBUART *s = CMSDK_APB_UART(obj);
 325
 326     memory_region_init_io(&s->iomem, obj, &uart_ops, s, "uart", 0x1000);
 327     sysbus_init_mmio(sbd, &s->iomem);
 328     sysbus_init_irq(sbd, &s->txint);
 329     sysbus_init_irq(sbd, &s->rxint);
 330     sysbus_init_irq(sbd, &s->txovrint);
 331     sysbus_init_irq(sbd, &s->rxovrint);
 332     sysbus_init_irq(sbd, &s->uartint);
 333 }
 334
 335 static void cmsdk_apb_uart_realize(DeviceState *dev, Error **errp)
 336 {
 337     CMSDKAPBUART *s = CMSDK_APB_UART(dev);
 338
 339     if (s->pclk_frq == 0) {
 340         error_setg(errp, "CMSDK APB UART: pclk-frq property must be set");
 341         return;
 342     }
 343
 344     /* This UART has no flow control, so we do not need to register
 345      * an event handler to deal with CHR_EVENT_BREAK.
 346      */
 347     qemu_chr_fe_set_handlers(&s->chr, uart_can_receive, uart_receive,
 348                              NULL, NULL, s, NULL, true);
 349 }
 350
 351 static int cmsdk_apb_uart_post_load(void *opaque, int version_id)
 352 {
 353     CMSDKAPBUART *s = CMSDK_APB_UART(opaque);
 354
 355     /* If we have a pending character, arrange to resend it. */
 356     if (s->state & R_STATE_TXFULL_MASK) {
 357         s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
 358                                              uart_transmit, s);
 359     }
 360     uart_update_parameters(s);
 361     return 0;
 362 }
 363
 364 static const VMStateDescription cmsdk_apb_uart_vmstate = {
 365     .name = "cmsdk-apb-uart",
 366     .version_id = 1,
 367     .minimum_version_id = 1,
 368     .post_load = cmsdk_apb_uart_post_load,
 369     .fields = (const VMStateField[]) {
 370         VMSTATE_UINT32(state, CMSDKAPBUART),
 371         VMSTATE_UINT32(ctrl, CMSDKAPBUART),
 372         VMSTATE_UINT32(intstatus, CMSDKAPBUART),
 373         VMSTATE_UINT32(bauddiv, CMSDKAPBUART),
 374         VMSTATE_UINT8(txbuf, CMSDKAPBUART),
 375         VMSTATE_UINT8(rxbuf, CMSDKAPBUART),
 376         VMSTATE_END_OF_LIST()
 377     }
 378 };
 379
 380 static Property cmsdk_apb_uart_properties[] = {
 381     DEFINE_PROP_CHR("chardev", CMSDKAPBUART, chr),
 382     DEFINE_PROP_UINT32("pclk-frq", CMSDKAPBUART, pclk_frq, 0),
 383     DEFINE_PROP_END_OF_LIST(),
 384 };
 385
 386 static void cmsdk_apb_uart_class_init(ObjectClass *klass, void *data)
 387 {
 388     DeviceClass *dc = DEVICE_CLASS(klass);
 389
 390     dc->realize = cmsdk_apb_uart_realize;
 391     dc->vmsd = &cmsdk_apb_uart_vmstate;
 392     dc->reset = cmsdk_apb_uart_reset;
 393     device_class_set_props(dc, cmsdk_apb_uart_properties);
 394 }
 395
 396 static const TypeInfo cmsdk_apb_uart_info = {
 397     .name = TYPE_CMSDK_APB_UART,
 398     .parent = TYPE_SYS_BUS_DEVICE,
 399     .instance_size = sizeof(CMSDKAPBUART),
 400     .instance_init = cmsdk_apb_uart_init,
 401     .class_init = cmsdk_apb_uart_class_init,
 402 };
 403
 404 static void cmsdk_apb_uart_register_types(void)
 405 {
 406     type_register_static(&cmsdk_apb_uart_info);
 407 }
 408
 409 type_init(cmsdk_apb_uart_register_types);