Re: [PATCH 2/2] serial: qcom-geni: Keep FIFO RX active during console TX

On 7/30/2026 3:14 AM, Bjorn Andersson wrote:
> 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 <[email protected]>
> ---
>   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

Nit: the SysRq handling here duplicates 
uart_unlock_and_check_sysrq_irqrestore(). I assume device_unlock() needs 
to use __uart_port_unlock_irqrestore(), which prevents reuse of the 
helper. A short comment documenting that constraint would help future 
readers understand the duplication.

Thanks,
Aniket

>   	__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
>