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AJvYcCV7CBrB9YRZzBtbbG49jjtTlLcFe5qhQ/N2tP7Udk0GXrZ2oDOgmw4tqk6eISso/jqv46CyoCItGSp2M+FraGIvW8X+ZykTAJXEUMDJ X-Gm-Message-State: AOJu0YzOOnfD/5vl494drIgh5sxTcYWQ2+rvnLD6G2eEH1Jho7sQ7F6a hEgzra72O8EgBNXyA7RejyYja0sD8f2aIkzbeNG6XSNasXQdaoHEq43SrOiWWg== X-Google-Smtp-Source: AGHT+IGwLF6m50OvfMrgXu5OtjFWL8dtO9YTmydt+ZsukEMXxXhyqzG9PSYlm5popmEqsreBccc6Gg== X-Received: by 2002:a17:902:c408:b0:1f3:29f1:76be with SMTP id d9443c01a7336-1f4497d8af4mr9107695ad.56.1716506562808; Thu, 23 May 2024 16:22:42 -0700 (PDT) Received: from dianders.sjc.corp.google.com ([2620:15c:9d:2:b835:ba86:8e6d:41c6]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1f44c797938sm1279545ad.64.2024.05.23.16.22.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 May 2024 16:22:42 -0700 (PDT) From: Douglas Anderson To: Greg Kroah-Hartman , Jiri Slaby Cc: Andy Shevchenko , John Ogness , Tony Lindgren , linux-arm-msm@vger.kernel.org, Johan Hovold , =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , Yicong Yang , Douglas Anderson , Guanbing Huang , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: [PATCH 1/2] serial: port: Don't block system suspend even if bytes are left to xmit Date: Thu, 23 May 2024 16:22:12 -0700 Message-ID: <20240523162207.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid> X-Mailer: git-send-email 2.45.1.288.g0e0cd299f1-goog In-Reply-To: <20240523232216.3148367-1-dianders@chromium.org> References: <20240523232216.3148367-1-dianders@chromium.org> Precedence: bulk X-Mailing-List: linux-serial@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 problem 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 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. 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 --- 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..b781227cc996 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 PM Runtime is + * enabled. Specifically PM Runtime 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 regulator PM Runtime 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);