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Thu, 10 Oct 2024 02:10:37 -0700 (PDT) From: Bartosz Golaszewski Date: Thu, 10 Oct 2024 11:10:25 +0200 Subject: [PATCH v2 4/6] gpio: cdev: put emitting the line state events on a workqueue Precedence: bulk X-Mailing-List: linux-gpio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241010-gpio-notify-in-kernel-events-v2-4-b560411f7c59@linaro.org> References: <20241010-gpio-notify-in-kernel-events-v2-0-b560411f7c59@linaro.org> In-Reply-To: <20241010-gpio-notify-in-kernel-events-v2-0-b560411f7c59@linaro.org> To: Linus Walleij , Bartosz Golaszewski , Kent Gibson Cc: linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4357; i=bartosz.golaszewski@linaro.org; h=from:subject:message-id; bh=sCvTb92VsU9o5sQdk/sTByAevcKbdTEudD1FU5KTG6Q=; b=owEBbQKS/ZANAwAKARGnLqAUcddyAcsmYgBnB5oHslqxMHergOZ85ymfnNVnjvhx3UNOSbjhy 2Tk58ON3MaJAjMEAAEKAB0WIQQWnetsC8PEYBPSx58Rpy6gFHHXcgUCZweaBwAKCRARpy6gFHHX cpHhD/9U+MxzygvDhzTtOpl7hxtef7JseBNg7YFZUWg3KraN6xZf2ymhT7rzcDY+X4/yhxSGLm2 beutzqT3WHKrBUJ+uNbipqgdi3i+W8CjU/pr1Ok1KWwjqPTJiWtWEtWnrbTA55n1wLAYiKPxLNj Gv8GmuK66jlM1tlJSo/FZkpU6dTi40qQqg4FGaJGci7CWj4HsB6rB6sh0Sqii40nqLXUsQbLA++ hzAL+Et9JLk1akIAWA9y3h4Dq8+lVuntGVWzJAkqvbIm5xbJL6xKXHjXKBqx/kNyGtuOcSnsIUQ Pknm5X74ARS926scOPe6N7KLI54Pu3ib/B+SD+aTKoT9VIRHRnS7fwWgfwQA/QN5s1G/mIfiqwZ zcfBu5hT+ct6hlZTB25+n39OUwmUQvI/YmN2liHsLwjtGg5fKlwpojb351lJQxohmnhf0TjsWKz 4UXNDuwnR4LmXIlRA2qY7SR5fr5AF4/3zBY/CAMTBslwDKbSKQUhUFbxFRlWw+JVbJvciWPJOrF vxuUQQq24KLXzoB6urAc1t6jr3uamnw92u0NKLcH1IiCl2YLwQEV5qWB1mto8PKbUtX+0tm/mKa Dcpp10U8G5Z/vkJpGSdCqk3mvjVQHpgEmzilP68dMZTtoixEh2UdHHi0G1FF7/lKFVTGsGi+gi0 AOz2k5r6wbw5zeQ== X-Developer-Key: i=bartosz.golaszewski@linaro.org; a=openpgp; fpr=169DEB6C0BC3C46013D2C79F11A72EA01471D772 From: Bartosz Golaszewski In order to allow line state notifications to be emitted from atomic context (for instance: from gpiod_direction_input/output()), we must stop calling any sleeping functions in lineinfo_changed_notify(). To that end let's use the new workqueue. Let's atomically allocate small structures containing the required data and fill it with information immediately upon being notified about the change except for the pinctrl state which will be retrieved later from process context. We can pretty reliably do this as pin functions are typically set once per boot. Let's make sure to bump the reference count of GPIO device and the GPIO character device file descriptor to keep both alive until the event was queued. Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib-cdev.c | 72 +++++++++++++++++++++++++++++++++++++-------- 1 file changed, 60 insertions(+), 12 deletions(-) diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index dec6c9a6005f..2677134b52cd 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -2451,6 +2451,7 @@ struct gpio_chardev_data { #ifdef CONFIG_GPIO_CDEV_V1 atomic_t watch_abi_version; #endif + struct file *fp; }; static int chipinfo_get(struct gpio_chardev_data *cdev, void __user *ip) @@ -2621,29 +2622,75 @@ static long gpio_ioctl_compat(struct file *file, unsigned int cmd, } #endif +struct lineinfo_changed_ctx { + struct work_struct work; + struct gpio_v2_line_info_changed chg; + struct gpio_device *gdev; + struct gpio_chardev_data *cdev; +}; + +static void lineinfo_changed_func(struct work_struct *work) +{ + struct lineinfo_changed_ctx *ctx = + container_of(work, struct lineinfo_changed_ctx, work); + struct gpio_chip *gc; + int ret; + + scoped_guard(srcu, &ctx->gdev->srcu) { + gc = srcu_dereference(ctx->gdev->chip, &ctx->gdev->srcu); + if (!gc) + return; + + /* + * We're doing this late because it's a sleeping function. Pin + * functions are in general much more static and while it's not + * 100% bullet-proof, it's good enough for most cases. + */ + if (!pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset)) + ctx->chg.info.flags |= GPIO_V2_LINE_FLAG_USED; + } + + ret = kfifo_in_spinlocked(&ctx->cdev->events, &ctx->chg, 1, + &ctx->cdev->wait.lock); + if (ret) + wake_up_poll(&ctx->cdev->wait, EPOLLIN); + else + pr_debug_ratelimited("lineinfo event FIFO is full - event dropped\n"); + + gpio_device_put(ctx->gdev); + fput(ctx->cdev->fp); + kfree(ctx); +} + static int lineinfo_changed_notify(struct notifier_block *nb, unsigned long action, void *data) { struct gpio_chardev_data *cdev = container_of(nb, struct gpio_chardev_data, lineinfo_changed_nb); - struct gpio_v2_line_info_changed chg; + struct lineinfo_changed_ctx *ctx; struct gpio_desc *desc = data; - int ret; if (!test_bit(gpio_chip_hwgpio(desc), cdev->watched_lines)) return NOTIFY_DONE; - memset(&chg, 0, sizeof(chg)); - chg.event_type = action; - chg.timestamp_ns = ktime_get_ns(); - gpio_desc_to_lineinfo(desc, &chg.info, false); - supinfo_to_lineinfo(desc, &chg.info); + ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC); + if (!ctx) { + pr_err("Failed to allocate memory for line info notification\n"); + return NOTIFY_DONE; + } - ret = kfifo_in_spinlocked(&cdev->events, &chg, 1, &cdev->wait.lock); - if (ret) - wake_up_poll(&cdev->wait, EPOLLIN); - else - pr_debug_ratelimited("lineinfo event FIFO is full - event dropped\n"); + ctx->chg.event_type = action; + ctx->chg.timestamp_ns = ktime_get_ns(); + gpio_desc_to_lineinfo(desc, &ctx->chg.info, true); + supinfo_to_lineinfo(desc, &ctx->chg.info); + /* Keep the GPIO device alive until we emit the event. */ + ctx->gdev = gpio_device_get(desc->gdev); + ctx->cdev = cdev; + /* Keep the file descriptor alive too. */ + get_file(ctx->cdev->fp); + + INIT_WORK(&ctx->work, lineinfo_changed_func); + queue_work(ctx->gdev->line_state_wq, &ctx->work); return NOTIFY_OK; } @@ -2803,6 +2850,7 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file) goto out_unregister_line_notifier; file->private_data = cdev; + cdev->fp = file; ret = nonseekable_open(inode, file); if (ret)