This change introduces pm_qos requests in the imx serial driver.
The idea is to skip deeper C-state in case we need a strict
latency requirement in the uart port. The latency is
computed based on the buffer size and the current baud rate.
We schedule a work queue to set the pm qos requirement.
Cc: Fabio Estevam <festevam@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxxx>
Cc: linux-serial@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Eduardo Valentin <edubezval@xxxxxxxxx>
---
drivers/tty/serial/imx.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index d9ccf6b..24ed0fa 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -42,6 +42,7 @@
#include <linux/pm.h>
#include <linux/pm_runtime.h>
#include <linux/pm_wakeup.h>
+#include <linux/pm_qos.h>
#include <asm/irq.h>
#include <linux/platform_data/serial-imx.h>
@@ -222,6 +223,10 @@ struct imx_port {
unsigned int saved_reg[10];
bool context_saved;
+ struct pm_qos_request pm_qos_request;
+ u32 latency;
+ u32 calc_latency;
+ struct work_struct qos_work;
bool is_suspending;
};
@@ -1320,6 +1325,14 @@ static void imx_flush_buffer(struct uart_port *port)
pm_runtime_put_autosuspend(sport->port.dev);
}
+static void serial_imx_uart_qos_work(struct work_struct *work)
+{
+ struct imx_port *sport = container_of(work, struct imx_port,
+ qos_work);
+
+ pm_qos_update_request(&sport->pm_qos_request, sport->latency);
+}
+
static void
imx_set_termios(struct uart_port *port, struct ktermios *termios,
struct ktermios *old)
@@ -1393,6 +1406,12 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
quot = uart_get_divisor(port, baud);
+ /* calculate wakeup latency constraint */
+ sport->calc_latency = (USEC_PER_SEC * sport->port.fifosize) /
+ (baud / 8);
+ sport->latency = sport->calc_latency;
+ schedule_work(&sport->qos_work);
+
spin_lock_irqsave(&sport->port.lock, flags);
sport->port.read_status_mask = 0;
@@ -2012,6 +2031,11 @@ static int serial_imx_probe(struct platform_device *pdev)
imx_ports[sport->port.line] = sport;
+ sport->latency = PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE;
+ sport->calc_latency = PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE;
+ pm_qos_add_request(&sport->pm_qos_request, PM_QOS_CPU_DMA_LATENCY,
+ sport->latency);
+ INIT_WORK(&sport->qos_work, serial_imx_uart_qos_work);
platform_set_drvdata(pdev, sport);
device_init_wakeup(sport->port.dev, true);
@@ -2041,6 +2065,7 @@ static int serial_imx_remove(struct platform_device *pdev)
clk_unprepare(sport->clk_per);
clk_unprepare(sport->clk_ipg);
ret = uart_remove_one_port(&imx_reg, &sport->port);
+ pm_qos_remove_request(&sport->pm_qos_request);
device_init_wakeup(&pdev->dev, false);
return ret;
@@ -2119,6 +2144,8 @@ static int serial_imx_runtime_suspend(struct device *dev)
serial_imx_save_context(sport);
serial_imx_enable_wakeup(sport, true);
+ sport->latency = PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE;
+ schedule_work(&sport->qos_work);
clk_disable(sport->clk_per);
clk_disable(sport->clk_ipg);
@@ -2140,6 +2167,8 @@ static int serial_imx_runtime_resume(struct device *dev)
}
serial_imx_enable_wakeup(sport, false);
+ sport->latency = sport->calc_latency;
+ schedule_work(&sport->qos_work);
serial_imx_restore_context(sport);
return 0;
--
2.5.0
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