hw/char/pl011: add a clock input

Add a clock input to the PL011 UART so we can compute the current baud
rate and trace it. This is intended for developers who wish to use QEMU
to e.g. debug their firmware or to figure out the baud rate configured
by an unknown/closed source binary.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Luc Michel <luc@lmichel.fr>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/char/pl011.c

@@ -22,6 +22,7 @@
 #include "hw/char/pl011.h"
 #include "hw/irq.h"
 #include "hw/sysbus.h"
+#include "hw/qdev-clock.h"
 #include "migration/vmstate.h"
 #include "chardev/char-fe.h"
 #include "qemu/log.h"
@@ -169,6 +170,25 @@ static void pl011_set_read_trigger(PL011State *s)
         s->read_trigger = 1;
 }
 
+static unsigned int pl011_get_baudrate(const PL011State *s)
+{
+    uint64_t clk;
+
+    if (s->fbrd == 0) {
+        return 0;
+    }
+
+    clk = clock_get_hz(s->clk);
+    return (clk / ((s->ibrd << 6) + s->fbrd)) << 2;
+}
+
+static void pl011_trace_baudrate_change(const PL011State *s)
+{
+    trace_pl011_baudrate_change(pl011_get_baudrate(s),
+                                clock_get_hz(s->clk),
+                                s->ibrd, s->fbrd);
+}
+
 static void pl011_write(void *opaque, hwaddr offset,
                         uint64_t value, unsigned size)
 {
@@ -198,9 +218,11 @@ static void pl011_write(void *opaque, hwaddr offset,
         break;
     case 9: /* UARTIBRD */
         s->ibrd = value;
+        pl011_trace_baudrate_change(s);
         break;
     case 10: /* UARTFBRD */
         s->fbrd = value;
+        pl011_trace_baudrate_change(s);
         break;
     case 11: /* UARTLCR_H */
         /* Reset the FIFO state on FIFO enable or disable */
@@ -286,12 +308,29 @@ static void pl011_event(void *opaque, QEMUChrEvent event)
         pl011_put_fifo(opaque, 0x400);
 }
 
+static void pl011_clock_update(void *opaque)
+{
+    PL011State *s = PL011(opaque);
+
+    pl011_trace_baudrate_change(s);
+}
+
 static const MemoryRegionOps pl011_ops = {
     .read = pl011_read,
     .write = pl011_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
 };
 
+static const VMStateDescription vmstate_pl011_clock = {
+    .name = "pl011/clock",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_CLOCK(clk, PL011State),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_pl011 = {
     .name = "pl011",
     .version_id = 2,
@@ -314,6 +353,10 @@ static const VMStateDescription vmstate_pl011 = {
         VMSTATE_INT32(read_count, PL011State),
         VMSTATE_INT32(read_trigger, PL011State),
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (const VMStateDescription * []) {
+        &vmstate_pl011_clock,
+        NULL
     }
 };
 
@@ -334,6 +377,8 @@ static void pl011_init(Object *obj)
         sysbus_init_irq(sbd, &s->irq[i]);
     }
 
+    s->clk = qdev_init_clock_in(DEVICE(obj), "clk", pl011_clock_update, s);
+
     s->read_trigger = 1;
     s->ifl = 0x12;
     s->cr = 0x300;

hw/char/trace-events

@@ -65,6 +65,7 @@ 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 0x%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"
+pl011_baudrate_change(unsigned int baudrate, uint64_t clock, uint32_t ibrd, uint32_t fbrd) "new baudrate %u (clk: %" PRIu64 "hz, ibrd: %" PRIu32 ", fbrd: %" PRIu32 ")"
 
 # 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"

include/hw/char/pl011.h

@@ -49,6 +49,7 @@ struct PL011State {
     int read_trigger;
     CharBackend chr;
     qemu_irq irq[6];
+    Clock *clk;
     const unsigned char *id;
 };