linux-kernel - [PATCH 7/8] serial: qcom-geni: disable interrupts during console writes

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Message-ID: <20240902152451.862-8-johan+linaro@kernel.org>
Date: Mon,  2 Sep 2024 17:24:50 +0200
From: Johan Hovold <johan+linaro@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Douglas Anderson <dianders@...omium.org>,
	'Nícolas F . R . A . Prado' <nfraprado@...labora.com>,
	linux-arm-msm@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>
Subject: [PATCH 7/8] serial: qcom-geni: disable interrupts during console writes

Disable the GENI interrupts during console writes to reduce the risk of
having interrupt handlers spinning on the port lock on other cores for
extended periods of time.

This can, for example, reduce the total amount of time spent in the
interrupt handler during boot of the x1e80100 CRD by up to a factor nine
(e.g. from 274 ms to 30 ms) while the worst case processing time drops
from 19 ms to 8 ms.

Fixes: c4f528795d1a ("tty: serial: msm_geni_serial: Add serial driver support for GENI based QUP")
Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index be620c5703f5..fbed143c90a3 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -488,6 +488,7 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
 {
 	struct uart_port *uport;
 	struct qcom_geni_serial_port *port;
+	u32 m_irq_en, s_irq_en;
 	bool locked = true;
 	unsigned long flags;
 
@@ -503,6 +504,11 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
 	else
 		uart_port_lock_irqsave(uport, &flags);
 
+	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);
+
 	if (qcom_geni_serial_main_active(uport)) {
 		/* Wait for completion or drain FIFO */
 		if (!locked || port->tx_remaining == 0)
@@ -515,6 +521,9 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
 
 	__qcom_geni_serial_console_write(uport, s, count);
 
+	writel(m_irq_en, uport->membase + SE_GENI_M_IRQ_EN);
+	writel(s_irq_en, uport->membase + SE_GENI_S_IRQ_EN);
+
 	if (locked)
 		uart_port_unlock_irqrestore(uport, flags);
 }
-- 
2.44.2