[SRU][O][PATCH v2 5/8] serial: qcom-geni: disable interrupts during console writes

[Juerg Haefliger]

From: Johan Hovold <johan+linaro at kernel.org>

BugLink: https://bugs.launchpad.net/bugs/2089237

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")
Reviewed-by: Douglas Anderson <dianders at chromium.org>
Tested-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>
Signed-off-by: Johan Hovold <johan+linaro at kernel.org>
Link: https://lore.kernel.org/r/20240906131336.23625-8-johan+linaro@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 6f3c3cafb115c72f9222295a556d62d5d1e00f7a)
Signed-off-by: Juerg Haefliger <juerg.haefliger at canonical.com>
---
 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 3acba0887fca..0682ba22210a 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -495,6 +495,7 @@ 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;
 
@@ -510,6 +511,11 @@ 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)
@@ -522,6 +528,9 @@ 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);
 }
-- 
2.43.0