linux-kernel - [PATCH] uio: use threaded interrupts

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Message-ID: <20240326195927.3265297-1-chris.packham@alliedtelesis.co.nz>
Date: Wed, 27 Mar 2024 08:59:27 +1300
From: Chris Packham <chris.packham@...iedtelesis.co.nz>
To: gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org,
	Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: [PATCH] uio: use threaded interrupts

Split the existing uio_interrupt into a hardirq handler and a thread
function. The hardirq handler deals with the interrupt source in
hardware, the thread function notifies userspace that there is an event
to be handled.

Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
---

Notes:
    I find myself needing to have a UIO interrupt associated with an
    interrupt pin on a PCA9539 (yes I know, it's a terrible chip but HW
    engineers love it because it's cheap).
    
    Prior to this the UIO registration fails with:
    
      [    6.484699] uio_pdrv_genirq detect-gpio-9: unable to register uio device
      [    6.484722] uio_pdrv_genirq detect-gpio-9: probe with driver uio_pdrv_genirq failed with error -22
    
    The -EINVAL ultimately comes from __setup_irq() where it knows the
    interrupt descriptor is nested but we haven't provided a thread_fn.

 drivers/uio/uio.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index bb77de6fa067..a86cf2e4f200 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -442,18 +442,27 @@ EXPORT_SYMBOL_GPL(uio_event_notify);
  * @irq: IRQ number, can be UIO_IRQ_CYCLIC for cyclic timer
  * @dev_id: Pointer to the devices uio_device structure
  */
-static irqreturn_t uio_interrupt(int irq, void *dev_id)
+static irqreturn_t uio_interrupt_handler(int irq, void *dev_id)
 {
 	struct uio_device *idev = (struct uio_device *)dev_id;
 	irqreturn_t ret;
 
 	ret = idev->info->handler(irq, idev->info);
 	if (ret == IRQ_HANDLED)
-		uio_event_notify(idev->info);
+		ret = IRQ_WAKE_THREAD;
 
 	return ret;
 }
 
+static irqreturn_t uio_interrupt_thread(int irq, void *dev_id)
+{
+	struct uio_device *idev = (struct uio_device *)dev_id;
+
+	uio_event_notify(idev->info);
+
+	return IRQ_HANDLED;
+}
+
 struct uio_listener {
 	struct uio_device *dev;
 	s32 event_count;
@@ -1024,8 +1033,8 @@ int __uio_register_device(struct module *owner,
 		 * FDs at the time of unregister and therefore may not be
 		 * freed until they are released.
 		 */
-		ret = request_irq(info->irq, uio_interrupt,
-				  info->irq_flags, info->name, idev);
+		ret = request_threaded_irq(info->irq, uio_interrupt_handler, uio_interrupt_thread,
+					   info->irq_flags, info->name, idev);
 		if (ret) {
 			info->uio_dev = NULL;
 			goto err_request_irq;
-- 
2.43.2