linux-kernel - [PATCH] serial: core: Fix runtime PM handling for pending tx

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Date:   Mon, 23 Oct 2023 10:48:54 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        Dhruva Gole <d-gole@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Richard Purdie <richard.purdie@...uxfoundation.org>,
        Bruce Ashfield <bruce.ashfield@...il.com>,
        Mikko Rapeli <mikko.rapeli@...aro.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Randy MacLeod <randy.macleod@...driver.com>
Subject: [PATCH] serial: core: Fix runtime PM handling for pending tx

Richard reported that a serial port may end up sometimes with tx data
pending in the buffer for long periods of time.

Turns out we bail out early on any errors from pm_runtime_get(),
including -EINPROGRESS. To fix the issue, we need to ignore -EINPROGRESS
as we only care about the runtime PM usage count at this point. We check
for an active runtime PM state later on for tx.

Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")
Reported-by: Richard Purdie <richard.purdie@...uxfoundation.org>
Cc: Bruce Ashfield <bruce.ashfield@...il.com>
Cc: Mikko Rapeli <mikko.rapeli@...aro.org>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Randy MacLeod <randy.macleod@...driver.com>
Signed-off-by: Tony Lindgren <tony@...mide.com>
---
 drivers/tty/serial/serial_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -146,7 +146,7 @@ static void __uart_start(struct uart_state *state)
 
 	/* Increment the runtime PM usage count for the active check below */
 	err = pm_runtime_get(&port_dev->dev);
-	if (err < 0) {
+	if (err < 0 && err != -EINPROGRESS) {
 		pm_runtime_put_noidle(&port_dev->dev);
 		return;
 	}
-- 
2.42.0