From nobody Tue Dec 16 19:40:52 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3967EE92702 for ; Thu, 5 Oct 2023 14:37:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236741AbjJEOg7 (ORCPT ); Thu, 5 Oct 2023 10:36:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46292 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236150AbjJEOej (ORCPT ); Thu, 5 Oct 2023 10:34:39 -0400 Received: from muru.com (muru.com [72.249.23.125]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 17C3A4233; Thu, 5 Oct 2023 06:53:03 -0700 (PDT) Received: from hillo.muru.com (localhost [127.0.0.1]) by muru.com (Postfix) with ESMTP id 51FE280A0; Thu, 5 Oct 2023 07:56:47 +0000 (UTC) From: Tony Lindgren To: Greg Kroah-Hartman , Jiri Slaby , Andy Shevchenko Cc: Andy Shevchenko , Dhruva Gole , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , John Ogness , Johan Hovold , Sebastian Andrzej Siewior , Vignesh Raghavendra , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Maximilian Luz Subject: [PATCH] serial: core: Fix checks for tx runtime PM state Date: Thu, 5 Oct 2023 10:56:42 +0300 Message-ID: <20231005075644.25936-1-tony@atomide.com> X-Mailer: git-send-email 2.42.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Maximilian reported that surface_serial_hub serdev tx does not work during system suspend. During system suspend, runtime PM gets disabled in __device_suspend_late(), and tx is unable to wake-up the serial core port device that we use to check if tx is safe to start. Johan summarized the regression noting that serdev tx no longer always works as earlier when the serdev device is runtime PM active. The serdev device and the serial core controller devices are siblings of the serial port hardware device. The runtime PM usage count from serdev device does not propagate to the serial core device siblings, it only propagates to the parent. In addition to the tx issue for suspend, testing for the serial core port device can cause an unnecessary delay in enabling tx while waiting for the serial core port device to wake-up. The serial core port device wake-up is only needed to flush pending tx when the serial port hardware device was in runtime PM suspended state. To fix the regression, we need to check the runtime PM state of the parent serial port hardware device for tx instead of the serial core port device. As the serial port device drivers may or may not implement runtime PM, we need to also add a check for pm_runtime_enabled(). Reported-by: Maximilian Luz Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to en= able runtime PM") Signed-off-by: Tony Lindgren Reviewed-by: Andy Shevchenko Tested-by: Maximilian Luz --- 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_c= ore.c --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -156,7 +156,7 @@ static void __uart_start(struct uart_state *state) * enabled, serial_port_runtime_resume() calls start_tx() again * after enabling the device. */ - if (pm_runtime_active(&port_dev->dev)) + if (!pm_runtime_enabled(port->dev) || pm_runtime_active(port->dev)) port->ops->start_tx(port); pm_runtime_mark_last_busy(&port_dev->dev); pm_runtime_put_autosuspend(&port_dev->dev); --=20 2.42.0