hw/char/imx_serial: Implement receive FIFO and ageing timer

This patch implements a 32 half word FIFO as per imx serial device
specifications.  If a non empty FIFO is below the trigger level, an
ageing timer will tick for a duration of 8 characters.  On expiry,
AGTIM will be set triggering an interrupt.  AGTIM timer resets when
there is activity in the receive FIFO.

Otherwise, RRDY is set when trigger level is exceeded.  The receive
trigger level is 8 in newer kernel versions and 1 in older ones.

This change will break migration compatibility for the imx boards.

Signed-off-by: Rayhan Faizel <rayhan.faizel@gmail.com>
Message-id: 20240125151931.83494-1-rayhan.faizel@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: commit message tidyups]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 89 insertions, 13 deletions

diff --git a/hw/char/imx_serial.c b/hw/char/imx_serial.c
index 1df862eb7f..ba37be6faa 100644
--- a/hw/char/imx_serial.c
+++ b/hw/char/imx_serial.c
@@ -26,6 +26,7 @@
 #include "migration/vmstate.h"
 #include "qemu/log.h"
 #include "qemu/module.h"
+#include "qemu/fifo32.h"
 
 #ifndef DEBUG_IMX_UART
 #define DEBUG_IMX_UART 0
@@ -41,10 +42,11 @@
 
 static const VMStateDescription vmstate_imx_serial = {
     .name = TYPE_IMX_SERIAL,
-    .version_id = 2,
-    .minimum_version_id = 2,
+    .version_id = 3,
+    .minimum_version_id = 3,
     .fields = (const VMStateField[]) {
-        VMSTATE_INT32(readbuff, IMXSerialState),
+        VMSTATE_FIFO32(rx_fifo, IMXSerialState),
+        VMSTATE_TIMER(ageing_timer, IMXSerialState),
         VMSTATE_UINT32(usr1, IMXSerialState),
         VMSTATE_UINT32(usr2, IMXSerialState),
         VMSTATE_UINT32(ucr1, IMXSerialState),
@@ -72,21 +74,76 @@ static void imx_update(IMXSerialState *s)
      */
     usr1 = s->usr1 & s->ucr1 & (USR1_TRDY | USR1_RRDY);
     /*
+     * Interrupt if AGTIM is set (ageing timer interrupt in RxFIFO)
+     */
+    usr1 |= (s->ucr2 & UCR2_ATEN) ? (s->usr1 & USR1_AGTIM) : 0;
+    /*
      * Bits that we want in USR2 are not as conveniently laid out,
      * unfortunately.
      */
     mask = (s->ucr1 & UCR1_TXMPTYEN) ? USR2_TXFE : 0;
     /*
      * TCEN and TXDC are both bit 3
+     * ORE and OREN are both bit 1
      * RDR and DREN are both bit 0
      */
-    mask |= s->ucr4 & (UCR4_WKEN | UCR4_TCEN | UCR4_DREN);
+    mask |= s->ucr4 & (UCR4_WKEN | UCR4_TCEN | UCR4_DREN | UCR4_OREN);
 
     usr2 = s->usr2 & mask;
 
     qemu_set_irq(s->irq, usr1 || usr2);
 }
 
+static void imx_serial_rx_fifo_push(IMXSerialState *s, uint32_t value)
+{
+    uint32_t pushed_value = value;
+    if (fifo32_is_full(&s->rx_fifo)) {
+        /* Set ORE if FIFO is already full */
+        s->usr2 |= USR2_ORE;
+    } else {
+        if (fifo32_num_used(&s->rx_fifo) == FIFO_SIZE - 1) {
+            /* Set OVRRUN on 32nd character in FIFO */
+            pushed_value |= URXD_ERR | URXD_OVRRUN;
+        }
+        fifo32_push(&s->rx_fifo, pushed_value);
+    }
+}
+
+static uint32_t imx_serial_rx_fifo_pop(IMXSerialState *s)
+{
+    if (fifo32_is_empty(&s->rx_fifo)) {
+        return 0;
+    }
+    return fifo32_pop(&s->rx_fifo);
+}
+
+static void imx_serial_rx_fifo_ageing_timer_int(void *opaque)
+{
+    IMXSerialState *s = (IMXSerialState *) opaque;
+    s->usr1 |= USR1_AGTIM;
+    imx_update(s);
+}
+
+static void imx_serial_rx_fifo_ageing_timer_restart(void *opaque)
+{
+    /*
+     * Ageing timer starts ticking when
+     * RX FIFO is non empty and below trigger level.
+     * Timer is reset if new character is received or
+     * a FIFO read occurs.
+     * Timer triggers an interrupt when duration of
+     * 8 characters has passed (assuming 115200 baudrate).
+     */
+    IMXSerialState *s = (IMXSerialState *) opaque;
+
+    if (!(s->usr1 & USR1_RRDY) && !(s->uts1 & UTS1_RXEMPTY)) {
+        timer_mod_ns(&s->ageing_timer,
+                     qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + AGE_DURATION_NS);
+    } else {
+        timer_del(&s->ageing_timer);
+    }
+}
+
 static void imx_serial_reset(IMXSerialState *s)
 {
 
@@ -102,7 +159,9 @@ static void imx_serial_reset(IMXSerialState *s)
     s->ucr3 = 0x700;
     s->ubmr = 0;
     s->ubrc = 4;
-    s->readbuff = URXD_ERR;
+
+    fifo32_reset(&s->rx_fifo);
+    timer_del(&s->ageing_timer);
 }
 
 static void imx_serial_reset_at_boot(DeviceState *dev)
@@ -125,20 +184,28 @@ static uint64_t imx_serial_read(void *opaque, hwaddr offset,
                                 unsigned size)
 {
     IMXSerialState *s = (IMXSerialState *)opaque;
-    uint32_t c;
+    uint32_t c, rx_used;
+    uint8_t rxtl = s->ufcr & TL_MASK;
 
     DPRINTF("read(offset=0x%" HWADDR_PRIx ")\n", offset);
 
     switch (offset >> 2) {
     case 0x0: /* URXD */
-        c = s->readbuff;
+        c = imx_serial_rx_fifo_pop(s);
         if (!(s->uts1 & UTS1_RXEMPTY)) {
             /* Character is valid */
             c |= URXD_CHARRDY;
-            s->usr1 &= ~USR1_RRDY;
-            s->usr2 &= ~USR2_RDR;
-            s->uts1 |= UTS1_RXEMPTY;
+            rx_used = fifo32_num_used(&s->rx_fifo);
+            /* Clear RRDY if below threshold */
+            if (rx_used < rxtl) {
+                s->usr1 &= ~USR1_RRDY;
+            }
+            if (rx_used == 0) {
+                s->usr2 &= ~USR2_RDR;
+                s->uts1 |= UTS1_RXEMPTY;
+            }
             imx_update(s);
+            imx_serial_rx_fifo_ageing_timer_restart(s);
             qemu_chr_fe_accept_input(&s->chr);
         }
         return c;
@@ -300,19 +367,24 @@ static void imx_serial_write(void *opaque, hwaddr offset,
 static int imx_can_receive(void *opaque)
 {
     IMXSerialState *s = (IMXSerialState *)opaque;
-    return !(s->usr1 & USR1_RRDY);
+    return s->ucr2 & UCR2_RXEN && fifo32_num_used(&s->rx_fifo) < FIFO_SIZE;
 }
 
 static void imx_put_data(void *opaque, uint32_t value)
 {
     IMXSerialState *s = (IMXSerialState *)opaque;
+    uint8_t rxtl = s->ufcr & TL_MASK;
 
     DPRINTF("received char\n");
+    imx_serial_rx_fifo_push(s, value);
+    if (fifo32_num_used(&s->rx_fifo) >= rxtl) {
+        s->usr1 |= USR1_RRDY;
+    }
+
+    imx_serial_rx_fifo_ageing_timer_restart(s);
 
-    s->usr1 |= USR1_RRDY;
     s->usr2 |= USR2_RDR;
     s->uts1 &= ~UTS1_RXEMPTY;
-    s->readbuff = value;
     if (value & URXD_BRK) {
         s->usr2 |= USR2_BRCD;
     }
@@ -345,6 +417,10 @@ static void imx_serial_realize(DeviceState *dev, Error **errp)
 {
     IMXSerialState *s = IMX_SERIAL(dev);
 
+    fifo32_create(&s->rx_fifo, FIFO_SIZE);
+    timer_init_ns(&s->ageing_timer, QEMU_CLOCK_VIRTUAL,
+                  imx_serial_rx_fifo_ageing_timer_int, s);
+
     DPRINTF("char dev for uart: %p\n", qemu_chr_fe_get_driver(&s->chr));
 
     qemu_chr_fe_set_handlers(&s->chr, imx_can_receive, imx_receive,