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dev/ns16550: Fix race condition in transmit path

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In SMP systems, the interrupt handler may run concurrently with tasks
trying to transmit.  Properly protect the transmit state through the
device lock.  Simplify the transmit process.

Close #5552.

Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
This commit is contained in:
Sebastian Huber
2026-04-17 01:16:09 +02:00
parent f22c306945
commit de8ef0424c
2 changed files with 28 additions and 39 deletions
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bsps/include/libchip/ns16550.h
+1 -4
View File
@@ -79,10 +79,7 @@ struct ns16550_context{
uint8_t modem_control;
uint8_t line_control;
uint32_t baud_divisor;
size_t out_total;
size_t out_remaining;
size_t out_current;
const char *out_buf;
size_t out_pending;
rtems_termios_tty *tty;
ns16550_calculate_baud_divisor calculate_baud_divisor;
};
bsps/shared/dev/serial/ns16550-context.c
+27 -35
View File
@@ -284,6 +284,8 @@ static void ns16550_isr(void *arg)
ns16550_get_reg get = ctx->get_reg;
int i = 0;
char buf [SP_FIFO_SIZE];
rtems_interrupt_lock_context lock_context;
size_t out_pending;
/* Iterate until no more interrupts are pending */
do {
@@ -300,19 +302,16 @@ static void ns16550_isr(void *arg)
rtems_termios_enqueue_raw_characters(tty, buf, i);
/* Do transmit */
if (ctx->out_total > 0
rtems_termios_device_lock_acquire(&ctx->base, &lock_context);
out_pending = ctx->out_pending;
if (out_pending > 0
&& (get(port, NS16550_LINE_STATUS) & SP_LSR_THOLD) != 0) {
size_t current = ctx->out_current;
ctx->out_pending = 0;
rtems_termios_device_lock_release(&ctx->base, &lock_context);
ctx->out_buf += current;
ctx->out_remaining -= current;
if (ctx->out_remaining > 0) {
ctx->out_current =
ns16550_write_to_fifo(ctx, ctx->out_buf, ctx->out_remaining);
} else {
rtems_termios_dequeue_characters(tty, ctx->out_total);
}
rtems_termios_dequeue_characters(tty, out_pending);
} else {
rtems_termios_device_lock_release(&ctx->base, &lock_context);
}
} while ((get( port, NS16550_INTERRUPT_ID) & SP_IID_0) == 0);
}
@@ -322,28 +321,25 @@ static void ns16550_isr_task(void *arg)
rtems_termios_tty *tty = arg;
ns16550_context *ctx = rtems_termios_get_device_context(tty);
uint8_t status = (*ctx->get_reg)(ctx->port, NS16550_LINE_STATUS);
rtems_interrupt_lock_context lock_context;
size_t out_pending;
if ((status & SP_LSR_RDY) != 0) {
ns16550_clear_and_set_interrupts(ctx, SP_INT_RX_ENABLE, 0);
rtems_termios_rxirq_occured(tty);
}
if (ctx->out_total > 0 && (status & SP_LSR_THOLD) != 0) {
size_t current = ctx->out_current;
rtems_termios_device_lock_acquire(&ctx->base, &lock_context);
out_pending = ctx->out_pending;
ctx->out_buf += current;
ctx->out_remaining -= current;
if (out_pending > 0 && (status & SP_LSR_THOLD) != 0) {
ctx->out_pending = 0;
rtems_termios_device_lock_release(&ctx->base, &lock_context);
if (ctx->out_remaining > 0) {
ctx->out_current =
ns16550_write_to_fifo(ctx, ctx->out_buf, ctx->out_remaining);
} else {
size_t done = ctx->out_total;
ctx->out_total = 0;
ns16550_clear_and_set_interrupts(ctx, SP_INT_TX_ENABLE, 0);
rtems_termios_dequeue_characters(tty, done);
}
ns16550_clear_and_set_interrupts(ctx, SP_INT_TX_ENABLE, 0);
rtems_termios_dequeue_characters(tty, out_pending);
} else {
rtems_termios_device_lock_release(&ctx->base, &lock_context);
}
}
@@ -781,12 +777,10 @@ static void ns16550_write_support_int(
{
ns16550_context *ctx = (ns16550_context *) base;
ctx->out_total = len;
if (len > 0) {
ctx->out_remaining = len;
ctx->out_buf = buf;
ctx->out_current = ns16550_write_to_fifo(ctx, buf, len);
if (ctx->out_pending == 0) {
ctx->out_pending = ns16550_write_to_fifo(ctx, buf, len);
}
ns16550_enable_interrupts(ctx, NS16550_ENABLE_ALL_INTR);
} else {
@@ -802,12 +796,10 @@ static void ns16550_write_support_task(
{
ns16550_context *ctx = (ns16550_context *) base;
ctx->out_total = len;
if (len > 0) {
ctx->out_remaining = len;
ctx->out_buf = buf;
ctx->out_current = ns16550_write_to_fifo(ctx, buf, len);
if (ctx->out_pending == 0) {
ctx->out_pending = ns16550_write_to_fifo(ctx, buf, len);
}
ns16550_clear_and_set_interrupts(ctx, 0, SP_INT_TX_ENABLE);
}