* Johan Hovold [off-list ref] [210923 12:50]:

On Tue, Sep 21, 2021 at 01:33:44PM +0300, Tony Lindgren wrote:

quoted

+static int serial8250_prep_tx(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	struct device *dev = up->port.dev;
+	int err;
+
+	if (!(up->capabilities & UART_CAP_RPM))
+		return 0;
+
+	if (!pm_runtime_suspended(dev)) {
+		pm_runtime_mark_last_busy(dev);
+		return 0;
+	}
+
+	err = pm_request_resume(dev);
+	if (err < 0) {
+		dev_warn(dev, "prep_tx wakeup failed: %d\n", err);
+		return err;
+	}

How is this supposed to work without a runtime PM usage-counter
increment? What's to prevent the port from suspending again while it's
transmitting?

Hmm yeah we should at pm_runtime_get() and pm_runtime_put() to write()
unless serial8250_rpm_get() and serial8250_rpm_put() are doing it.

Or pair prep with finish and deal with the usage count there.

Regards,

Tony