[PATCH 2/2] serial: qcom-geni: Keep FIFO RX active during console TX
From: Bjorn Andersson
Date: Wed Jul 29 2026 - 17:53:44 EST
The GENI main sequencer handles console TX while the secondary sequencer
handles FIFO RX. Before nbcon, the legacy console writer disabled both
interrupt domains while it performed a long polled M-side transfer. This
left the small S-side FIFO unserviced, allowing console input to overrun
and be lost.
The nbcon conversion replaces IRQ masking with the UART port lock, but a
threaded console write still prevents the RX handler from draining the
FIFO. Keep S-side RX enabled independently of M-side TX and drain it
while refilling each bounded console command. This preserves interactive
input during console output.
Atomic output masks only M-side TX state, leaving FIFO RX handling
independent. The threaded writer can also detect a SysRq character while
it drains RX, so defer delivery until device_unlock() drops the UART port
lock, as the existing IRQ path does with uart_unlock_and_check_sysrq().
Assisted-by: OpenCode:GPT-5.5
Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxxxx>
---
drivers/tty/serial/qcom_geni_serial.c | 112 +++++++++++++++++++++++-----------
1 file changed, 75 insertions(+), 37 deletions(-)
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 08427390c173..a473d5521067 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -173,6 +173,7 @@ static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport);
static int qcom_geni_serial_port_setup(struct uart_port *uport);
static void qcom_geni_serial_start_tx_fifo(struct uart_port *uport);
static void qcom_geni_serial_resume_tx(struct uart_port *uport);
+static void qcom_geni_serial_poll_rx_fifo_locked(struct uart_port *uport);
static inline struct qcom_geni_serial_port *to_dev_port(struct uart_port *uport)
{
@@ -493,7 +494,7 @@ static void qcom_geni_serial_wr_char(struct uart_port *uport, unsigned char ch)
static void
__qcom_geni_serial_console_write(struct uart_port *uport, const char *s,
- unsigned int count)
+ unsigned int count, bool poll_rx)
{
struct qcom_geni_private_data *private_data = uport->private_data;
@@ -525,6 +526,8 @@ __qcom_geni_serial_console_write(struct uart_port *uport, const char *s,
if (!qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
M_TX_FIFO_WATERMARK_EN, true))
break;
+ if (poll_rx)
+ qcom_geni_serial_poll_rx_fifo_locked(uport);
chars_to_write = min_t(size_t, count - i, avail / 2);
uart_console_write(uport, s + i, chars_to_write,
qcom_geni_serial_wr_char);
@@ -593,7 +596,7 @@ static void qcom_geni_serial_console_write_thread(struct console *co,
return;
__qcom_geni_serial_console_write(uport, wctxt->outbuf + offset,
- count);
+ count, true);
offset += count;
if (!nbcon_exit_unsafe(wctxt))
@@ -612,7 +615,7 @@ static void qcom_geni_serial_console_write_atomic(struct console *co,
{
struct qcom_geni_serial_port *port;
struct uart_port *uport;
- u32 m_irq_en, s_irq_en;
+ u32 m_irq_en;
port = get_port_from_line(co->index, true, NULL);
if (IS_ERR(port))
@@ -623,15 +626,14 @@ static void qcom_geni_serial_console_write_atomic(struct console *co,
return;
m_irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
- s_irq_en = readl(uport->membase + SE_GENI_S_IRQ_EN);
- writel(0, uport->membase + SE_GENI_M_IRQ_EN);
- writel(0, uport->membase + SE_GENI_S_IRQ_EN);
+ writel(m_irq_en & ~(M_CMD_DONE_EN | M_TX_FIFO_WATERMARK_EN),
+ uport->membase + SE_GENI_M_IRQ_EN);
+ /* Atomic console output takes priority over an active normal TX command. */
qcom_geni_serial_console_takeover(uport, false);
- __qcom_geni_serial_console_write(uport, wctxt->outbuf, wctxt->len);
+ __qcom_geni_serial_console_write(uport, wctxt->outbuf, wctxt->len, false);
writel(m_irq_en, uport->membase + SE_GENI_M_IRQ_EN);
- writel(s_irq_en, uport->membase + SE_GENI_S_IRQ_EN);
nbcon_exit_unsafe(wctxt);
/* Restart TTY data left queued when atomic output canceled M TX. */
@@ -655,12 +657,25 @@ static void qcom_geni_serial_console_device_unlock(struct console *co,
unsigned long flags)
{
struct qcom_geni_serial_port *port;
+#ifdef CONFIG_MAGIC_SYSRQ_SERIAL
+ u8 sysrq_ch;
+#endif
port = get_port_from_line(co->index, true, NULL);
if (IS_ERR(port))
return;
+#ifdef CONFIG_MAGIC_SYSRQ_SERIAL
+ /* The threaded console writer can receive a SysRq character. */
+ sysrq_ch = port->uport.sysrq_ch;
+ port->uport.sysrq_ch = 0;
+#endif
__uart_port_unlock_irqrestore(&port->uport, flags);
+
+#ifdef CONFIG_MAGIC_SYSRQ_SERIAL
+ if (sysrq_ch)
+ handle_sysrq(sysrq_ch);
+#endif
}
static void handle_rx_console(struct uart_port *uport, u32 bytes, bool drop)
@@ -902,6 +917,34 @@ static void qcom_geni_serial_handle_rx_fifo(struct uart_port *uport, bool drop)
handle_rx_console(uport, total_bytes, drop);
}
+/* Caller holds the UART port lock. */
+static void qcom_geni_serial_poll_rx_fifo_locked(struct uart_port *uport)
+{
+ struct qcom_geni_serial_port *port = to_dev_port(uport);
+ struct tty_port *tport = &uport->state->port;
+ u32 s_irq_status;
+ bool drop_rx = false;
+
+ s_irq_status = readl(uport->membase + SE_GENI_S_IRQ_STATUS);
+ writel(s_irq_status, uport->membase + SE_GENI_S_IRQ_CLEAR);
+
+ if (s_irq_status & S_RX_FIFO_WR_ERR_EN) {
+ uport->icount.overrun++;
+ tty_insert_flip_char(tport, 0, TTY_OVERRUN);
+ }
+
+ if (s_irq_status & (S_GP_IRQ_0_EN | S_GP_IRQ_1_EN)) {
+ if (s_irq_status & S_GP_IRQ_0_EN)
+ uport->icount.parity++;
+ drop_rx = true;
+ } else if (s_irq_status & (S_GP_IRQ_2_EN | S_GP_IRQ_3_EN)) {
+ uport->icount.brk++;
+ port->brk = true;
+ }
+
+ qcom_geni_serial_handle_rx_fifo(uport, drop_rx);
+}
+
static void qcom_geni_serial_stop_rx_fifo(struct uart_port *uport)
{
u32 irq_en;
@@ -912,10 +955,6 @@ static void qcom_geni_serial_stop_rx_fifo(struct uart_port *uport)
irq_en &= ~(S_RX_FIFO_WATERMARK_EN | S_RX_FIFO_LAST_EN);
writel(irq_en, uport->membase + SE_GENI_S_IRQ_EN);
- irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
- irq_en &= ~(M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN);
- writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
-
if (!qcom_geni_serial_secondary_active(uport))
return;
@@ -949,10 +988,6 @@ static void qcom_geni_serial_start_rx_fifo(struct uart_port *uport)
irq_en = readl(uport->membase + SE_GENI_S_IRQ_EN);
irq_en |= S_RX_FIFO_WATERMARK_EN | S_RX_FIFO_LAST_EN;
writel(irq_en, uport->membase + SE_GENI_S_IRQ_EN);
-
- irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
- irq_en |= M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN;
- writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
}
static void qcom_geni_serial_stop_rx_dma(struct uart_port *uport)
@@ -1182,25 +1217,11 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
uart_port_lock(uport);
- m_irq_status = readl(uport->membase + SE_GENI_M_IRQ_STATUS);
s_irq_status = readl(uport->membase + SE_GENI_S_IRQ_STATUS);
- dma_tx_status = readl(uport->membase + SE_DMA_TX_IRQ_STAT);
dma_rx_status = readl(uport->membase + SE_DMA_RX_IRQ_STAT);
- geni_status = readl(uport->membase + SE_GENI_STATUS);
- dma = readl(uport->membase + SE_GENI_DMA_MODE_EN);
- m_irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
-
- trace_geni_serial_irq(uport->dev, m_irq_status, s_irq_status,
- dma_tx_status, dma_rx_status);
-
- writel(m_irq_status, uport->membase + SE_GENI_M_IRQ_CLEAR);
writel(s_irq_status, uport->membase + SE_GENI_S_IRQ_CLEAR);
- writel(dma_tx_status, uport->membase + SE_DMA_TX_IRQ_CLR);
writel(dma_rx_status, uport->membase + SE_DMA_RX_IRQ_CLR);
- if (WARN_ON(m_irq_status & M_ILLEGAL_CMD_EN))
- goto out_unlock;
-
if (s_irq_status & S_RX_FIFO_WR_ERR_EN) {
uport->icount.overrun++;
tty_insert_flip_char(tport, 0, TTY_OVERRUN);
@@ -1215,12 +1236,35 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
port->brk = true;
}
+ m_irq_status = readl(uport->membase + SE_GENI_M_IRQ_STATUS);
+ dma_tx_status = readl(uport->membase + SE_DMA_TX_IRQ_STAT);
+ geni_status = readl(uport->membase + SE_GENI_STATUS);
+ dma = readl(uport->membase + SE_GENI_DMA_MODE_EN);
+ m_irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
+
+ trace_geni_serial_irq(uport->dev, m_irq_status, s_irq_status,
+ dma_tx_status, dma_rx_status);
+
+ writel(m_irq_status, uport->membase + SE_GENI_M_IRQ_CLEAR);
+ writel(dma_tx_status, uport->membase + SE_DMA_TX_IRQ_CLR);
+
+ if (WARN_ON(m_irq_status & M_ILLEGAL_CMD_EN))
+ goto handle_rx;
+
if (dma) {
if (dma_tx_status & TX_DMA_DONE) {
qcom_geni_serial_handle_tx_dma(uport);
qcom_geni_set_rs485_mode(uport, SER_RS485_RTS_AFTER_SEND);
+ }
+ } else if (m_irq_status & m_irq_en &
+ (M_TX_FIFO_WATERMARK_EN | M_CMD_DONE_EN)) {
+ qcom_geni_serial_handle_tx_fifo(uport,
+ m_irq_status & M_CMD_DONE_EN,
+ geni_status & M_GENI_CMD_ACTIVE);
}
+handle_rx:
+ if (dma) {
if (dma_rx_status) {
if (dma_rx_status & RX_RESET_DONE)
goto out_unlock;
@@ -1237,12 +1281,6 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
qcom_geni_serial_handle_rx_dma(uport, drop_rx);
}
} else {
- if (m_irq_status & m_irq_en &
- (M_TX_FIFO_WATERMARK_EN | M_CMD_DONE_EN))
- qcom_geni_serial_handle_tx_fifo(uport,
- m_irq_status & M_CMD_DONE_EN,
- geni_status & M_GENI_CMD_ACTIVE);
-
if (s_irq_status & (S_RX_FIFO_WATERMARK_EN | S_RX_FIFO_LAST_EN))
qcom_geni_serial_handle_rx_fifo(uport, drop_rx);
}
@@ -1632,7 +1670,7 @@ static void qcom_geni_serial_earlycon_write(struct console *con,
{
struct earlycon_device *dev = con->data;
- __qcom_geni_serial_console_write(&dev->port, s, n);
+ __qcom_geni_serial_console_write(&dev->port, s, n, false);
}
#ifdef CONFIG_CONSOLE_POLL
--
2.53.0