From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1525210277; cv=none; d=google.com; s=arc-20160816; b=RkwzQO33jR+REfU49b+xuGL0moiAWe7kpyfzys/BjZaE2iHJpFt2s2lPqTQee+3M37 q9ByAXXQi1LDUEaahwSg5Hxu4EEpxhx1hqyro/mf/5ytumZy1D/UBpaviQPX/hVFAGAX yu/Gwzg4vQBPQF2EUMivOVdOpnVXDwAA6k0Tdf1mBzXjo8utAFg/8IpS580s1ahiW12R OWgx5xi9WRXlw8rVMvOM3IVMl9cdCqlxX+8FtpP22tXkxorfe17cMbzQX6yLjhwdFhdt dmVZdhJSiohQYwL/Pkz/hlM1Y9XLqE3ZMjw/uxkNAGM8nUsNCkEWFTuNx1u0gh+W/V1O xLwQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=message-id:date:subject:cc:to:from:arc-authentication-results; bh=3cYFgsswRS+nQtL2/pArPQ1MvoY0ti57mnwCmOACsCY=; b=QsZk9onYSsjeO8U3IzAU+QbkNk/nq9/gJbq7Pcphg+IL6ojbn8uS9rPyW60hsdc2bT smtLtnJsBY3yM5wlj8zyYqVPK4zJE8BtyIKOP4zTAKZ5bodLM+2UwcDqHXSK7RM2ltzP hAnoYm8ba1N0psr8vyZUxYrO9HTOnJy7HhSjg/d49ZWMozKJaKIjxMxp5/XXwhUAst3Q 7RckRdop1sDwHozZhJCOg4sl4o7k1D66qf16FNo3a1cIthQ9rI03Wp4jbHDQ88YDHjTK Qz72aVLy4kHfOybSt5JcSr/PVmi4IRkfKZQTKsXQ68Rf8kJ6WYRU1zBxrJpQTyqg3PVC 7jug== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of robherring2@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=robherring2@gmail.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of robherring2@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=robherring2@gmail.com X-Google-Smtp-Source: AB8JxZovskANJQnQLUUqoUbkp/zbZK+NEoAGuxo0yUVOHBFtDRWWwFLA9XgbZsaJ0wWX//DXk6Wkww== From: Rob Herring To: linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Cc: Greg Kroah-Hartman , Grant Likely , Linus Walleij , Mark Brown , Stephen Boyd , boot-architecture@lists.linaro.org, linux-arm-kernel@lists.infradead.org, Alexander Graf Subject: [RFC PATCH] driver core: make deferring probe forever optional Date: Tue, 1 May 2018 16:31:14 -0500 Message-Id: <20180501213114.20183-1-robh@kernel.org> X-Mailer: git-send-email 2.17.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1599298891509345819?= X-GMAIL-MSGID: =?utf-8?q?1599298891509345819?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Deferred probe will currently wait forever on dependent devices to probe, but sometimes a driver will never exist. It's also not always critical for a driver to exist. Platforms can rely on default configuration from the bootloader or reset defaults for things such as pinctrl and power domains. This is often the case with initial platform support until various drivers get enabled. There's at least 2 scenarios where deferred probe can render a platform broken. Both involve using a DT which has more devices and dependencies than the kernel supports. The 1st case is a driver may be disabled in the kernel config. The 2nd case is the kernel version may simply not have the dependent driver. This can happen if using a newer DT (provided by firmware perhaps) with a stable kernel version. Unfortunately, this change breaks with modules as we have no way of knowing when modules are done loading. One possibility is to make this opt in or out based on compatible strings rather than at a subsystem level. Ideally this information could be extracted automatically somehow. OTOH, maybe the lists are pretty small. There's only a handful of subsystems that can be optional, and then only so many drivers in those that can be modules (at least for pinctrl, many drivers are built-in only). Cc: Alexander Graf Signed-off-by: Rob Herring --- This patch came out of a discussion on the ARM boot-architecture list[1] about DT forwards and backwards compatibility issues. There are issues with newer DTs breaking on older, stable kernels. Some of these are difficult to solve, but cases of optional devices not having kernel support should be solvable. I tested this on a RPi3 B with the pinctrl driver forced off. With this change, the MMC/SD and UART drivers can function without the pinctrl driver. Rob [1] https://lists.linaro.org/pipermail/boot-architecture/2018-April/000466.html drivers/base/dd.c | 16 ++++++++++++++++ drivers/pinctrl/devicetree.c | 2 +- include/linux/device.h | 2 ++ 3 files changed, 19 insertions(+), 1 deletion(-) diff --git a/drivers/base/dd.c b/drivers/base/dd.c index c9f54089429b..5848808b9d7a 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -226,6 +226,15 @@ void device_unblock_probing(void) driver_deferred_probe_trigger(); } + +int driver_deferred_probe_optional(void) +{ + if (initcalls_done) + return -ENODEV; + + return -EPROBE_DEFER; +} + /** * deferred_probe_initcall() - Enable probing of deferred devices * @@ -240,6 +249,13 @@ static int deferred_probe_initcall(void) /* Sort as many dependencies as possible before exiting initcalls */ flush_work(&deferred_probe_work); initcalls_done = true; + + /* + * Trigger deferred probe again, this time we won't defer anything + * that is optional + */ + driver_deferred_probe_trigger(); + flush_work(&deferred_probe_work); return 0; } late_initcall(deferred_probe_initcall); diff --git a/drivers/pinctrl/devicetree.c b/drivers/pinctrl/devicetree.c index b601039d6c69..096e52a5c506 100644 --- a/drivers/pinctrl/devicetree.c +++ b/drivers/pinctrl/devicetree.c @@ -120,7 +120,7 @@ static int dt_to_map_one_config(struct pinctrl *p, np_config); of_node_put(np_pctldev); /* OK let's just assume this will appear later then */ - return -EPROBE_DEFER; + return driver_deferred_probe_optional(); } /* If we're creating a hog we can use the passed pctldev */ if (pctldev && (np_pctldev == p->dev->of_node)) diff --git a/include/linux/device.h b/include/linux/device.h index 0059b99e1f25..8de920442bc1 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -332,6 +332,8 @@ struct device *driver_find_device(struct device_driver *drv, struct device *start, void *data, int (*match)(struct device *dev, void *data)); +int driver_deferred_probe_optional(void); + /** * struct subsys_interface - interfaces to device functions * @name: name of the device function -- 2.17.0