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AJvYcCXon4Nmb5kMciQxPKeUdLTTNwU7MpCobZsjnixc0ofuWjWhH0Nmz2hebFtOn+NdataANtpvQ7pI9c64wFrXFmL0DvtdTrPB/N/+8jHC X-Gm-Message-State: AOJu0Yxhn0YWi5PYvzDK0ab83D8pv8LO5OWmAUsL16ayfJ5v9ti3pw1K 35wUFcCXAZC77MAce3nCUmLOLV9rJ80iHJdyPgquS/cW/g2ckk4Um99e+b/j4Q== X-Google-Smtp-Source: AGHT+IF0dfrykqzmUvNhdjADW7h9n7zm7Vm0UiyRN3i+/5G4mCKeIjmvMB7zJv32Mh9bRCpkaz5h1A== X-Received: by 2002:a05:6a00:1905:b0:6ec:e785:98b9 with SMTP id d2e1a72fcca58-70247899ea5mr2712668b3a.27.1717168205237; Fri, 31 May 2024 08:10:05 -0700 (PDT) Received: from dianders.sjc.corp.google.com ([2620:15c:9d:2:6c7c:c1c7:e465:4f2f]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70242b2bfc6sm1484111b3a.193.2024.05.31.08.10.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 May 2024 08:10:04 -0700 (PDT) From: Douglas Anderson To: Greg Kroah-Hartman , Jiri Slaby Cc: =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , Andy Shevchenko , John Ogness , Yicong Yang , Johan Hovold , linux-arm-msm@vger.kernel.org, Tony Lindgren , Douglas Anderson , stable@vger.kernel.org, Tony Lindgren , Bing Fan , Guanbing Huang , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: [PATCH v3] serial: port: Don't block system suspend even if bytes are left to xmit Date: Fri, 31 May 2024 08:09:18 -0700 Message-ID: <20240531080914.v3.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid> X-Mailer: git-send-email 2.45.1.288.g0e0cd299f1-goog 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 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") Cc: stable@vger.kernel.org Reviewed-by: Tony Lindgren Signed-off-by: Douglas Anderson --- 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 v3: - Adjust comment as per Tony Lindgren. - Add Cc: stable. 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 | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c index 91a338d3cb34..d35f1d24156c 100644 --- a/drivers/tty/serial/serial_port.c +++ b/drivers/tty/serial/serial_port.c @@ -64,6 +64,13 @@ static int serial_port_runtime_suspend(struct device *dev) if (port->flags & UPF_DEAD) return 0; + /* + * Nothing to do on pm_runtime_force_suspend(), see + * DEFINE_RUNTIME_DEV_PM_OPS. + */ + if (!pm_runtime_enabled(dev)) + return 0; + uart_port_lock_irqsave(port, &flags); if (!port_dev->tx_enabled) { uart_port_unlock_irqrestore(port, flags);