From fa38869b0161484f28a7e1f34535d5825dca6488 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Uwe=20Kleine-K=C3=B6nig?= Date: Mon, 20 Aug 2018 08:32:53 +0200 Subject: [PATCH] gpiolib: Don't support irq sharing for userspace MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This concerns gpio edge detection for GPIO IRQs used from userspace for GPIO event listeners. Trying to work out the right event if it's not sure that the examined gpio actually moved is impossible. Consider two gpios "gpioA" and "gpioB" that share an interrupt. gpioA's irq should trigger on any edge, gpioB's on a falling edge. If now the common irq fires and both gpio lines are high, there are several possibilities that could have happend: a) gpioA just had a low-to-high edge b) gpioB just had a high-to-low-to-high spike c) a combination of both a) and b) While c) is unlikely (in most setups) a) and b) alone are bad enough. Currently the code assumes case a) unconditionally and doesn't report an event for gpioB. Note that even if there is no irq sharing involved a spike for a gpio might not result in an event if it's configured to trigger for a single edge only. The only way to improve this is to drop support for interrupt sharing. This way a spike results in an event for the right gpio at least. Note that apart from dropping IRQF_SHARED this effectively undoes commit df1e76f28ffe ("gpiolib: skip unwanted events, don't convert them to opposite edge"). This obviously breaks setups that rely on interrupt sharing, but given that this cannot be reliable, this is probably an acceptable trade-off. Signed-off-by: Uwe Kleine-König [Assuming there are no users of interrupt sharing yet] Signed-off-by: Linus Walleij --- drivers/gpio/gpiolib.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index efce534a269b..8fbaea52bc1b 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -812,26 +812,26 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p) { struct lineevent_state *le = p; struct gpioevent_data ge; - int ret, level; + int ret; /* Do not leak kernel stack to userspace */ memset(&ge, 0, sizeof(ge)); ge.timestamp = le->timestamp; - level = gpiod_get_value_cansleep(le->desc); if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE && le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE) { + int level = gpiod_get_value_cansleep(le->desc); if (level) /* Emit low-to-high event */ ge.id = GPIOEVENT_EVENT_RISING_EDGE; else /* Emit high-to-low event */ ge.id = GPIOEVENT_EVENT_FALLING_EDGE; - } else if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE && level) { + } else if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE) { /* Emit low-to-high event */ ge.id = GPIOEVENT_EVENT_RISING_EDGE; - } else if (le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE && !level) { + } else if (le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE) { /* Emit high-to-low event */ ge.id = GPIOEVENT_EVENT_FALLING_EDGE; } else { @@ -942,7 +942,6 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip) if (eflags & GPIOEVENT_REQUEST_FALLING_EDGE) irqflags |= IRQF_TRIGGER_FALLING; irqflags |= IRQF_ONESHOT; - irqflags |= IRQF_SHARED; INIT_KFIFO(le->events); init_waitqueue_head(&le->wait); -- 2.30.2