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AJvYcCXn23W8k02vmcOOa1lOgLMLcrFK4fWLlEn1qAakIml+ueMrcn3kHhNTeGw//zBw7BRXv6GJxz2uwiyYshrQVB6l2/5WVmbtk+xxoINt5Q== X-Gm-Message-State: AOJu0YzrX5mnKP4Ncrd0hNrxHzvssSfZsBdZIyCfB1SxjTOTnuA8YIAp 395a6Urz5rWW1pY7zWYzdAjCqCF5CrMF0yt7vesKnujGamgFmoeCYDo/3VPRDg== X-Google-Smtp-Source: AGHT+IGn2tzzPa7fMTUghoHMSFR9I59iuxYacjgwwItgbhIUyfqhgbSLtvHe2FUJBmr5tdAjh0x3OQ== X-Received: by 2002:a17:902:d512:b0:1f3:1200:ceb3 with SMTP id d9443c01a7336-1f619b2cd29mr28968425ad.51.1717084146231; Thu, 30 May 2024 08:49:06 -0700 (PDT) Received: from dianders.sjc.corp.google.com ([2620:15c:9d:2:564b:72b6:4827:cf6a]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1f44c994a66sm120156915ad.182.2024.05.30.08.49.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 May 2024 08:49:05 -0700 (PDT) From: Douglas Anderson To: Greg Kroah-Hartman , Jiri Slaby Cc: Johan Hovold , Yicong Yang , Andy Shevchenko , =?utf-8?q?Uwe_Kleine-K?= =?utf-8?q?=C3=B6nig?= , John Ogness , linux-arm-msm@vger.kernel.org, Tony Lindgren , Douglas Anderson , Guanbing Huang , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: [PATCH v2] serial: port: Don't block system suspend even if bytes are left to xmit Date: Thu, 30 May 2024 08:48:46 -0700 Message-ID: <20240530084841.v2.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid> X-Mailer: git-send-email 2.45.1.288.g0e0cd299f1-goog Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Recently, suspend testing on sc7180-trogdor based devices has started to sometimes fail with messages like this: port a88000.serial:0.0: PM: calling pm_runtime_force_suspend+0x0/0xf8 @ 28934, parent: a88000.serial:0 port a88000.serial:0.0: PM: dpm_run_callback(): pm_runtime_force_suspend+0x0/0xf8 returns -16 port a88000.serial:0.0: PM: pm_runtime_force_suspend+0x0/0xf8 returned -16 after 33 usecs port a88000.serial:0.0: PM: failed to suspend: error -16 I could reproduce these problems by logging in via an agetty on the debug serial port (which was _not_ used for kernel console) and running: cat /var/log/messages ...and then (via an SSH session) forcing a few suspend/resume cycles. Tracing through the code and doing some printf()-based debugging shows that the -16 (-EBUSY) comes from the recently added serial_port_runtime_suspend(). The idea of the serial_port_runtime_suspend() function is to prevent the port from being _runtime_ suspended if it still has bytes left to transmit. Having bytes left to transmit isn't a reason to block _system_ suspend, though. If a serdev device in the kernel needs to block system suspend it should block its own suspend and it can use serdev_device_wait_until_sent() to ensure bytes are sent. The DEFINE_RUNTIME_DEV_PM_OPS() used by the serial_port code means that the system suspend function will be pm_runtime_force_suspend(). In pm_runtime_force_suspend() we can see that before calling the runtime suspend function we'll call pm_runtime_disable(). This should be a reliable way to detect that we're called from system suspend and that we shouldn't look for busyness. Fixes: 43066e32227e ("serial: port: Don't suspend if the port is still busy") Signed-off-by: Douglas Anderson Reviewed-by: Tony Lindgren --- In v1 [1] this was part of a 2-patch series. I'm now just sending this patch on its own since the Qualcomm GENI serial driver has ended up having a whole pile of problems that are taking a while to unravel. It makes sense to disconnect the two efforts. The core problem fixed by this patch and the geni problems never had any dependencies anyway. [1] https://lore.kernel.org/r/20240523162207.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid/ Changes in v2: - Fix "regulator" => "regular" in comment. - Fix "PM Runtime" => "runtime PM" in comment. - Commit messages says how serdev devices should ensure bytes xfered. drivers/tty/serial/serial_port.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c index 91a338d3cb34..93ca94426162 100644 --- a/drivers/tty/serial/serial_port.c +++ b/drivers/tty/serial/serial_port.c @@ -64,6 +64,16 @@ static int serial_port_runtime_suspend(struct device *dev) if (port->flags & UPF_DEAD) return 0; + /* + * We only want to check the busyness of the port if runtime PM is + * enabled. Specifically runtime PM will be disabled by + * pm_runtime_force_suspend() during system suspend and we don't want + * to block system suspend even if there is data still left to + * transmit. We only want to block regular runtime PM transitions. + */ + if (!pm_runtime_enabled(dev)) + return 0; + uart_port_lock_irqsave(port, &flags); if (!port_dev->tx_enabled) { uart_port_unlock_irqrestore(port, flags);