[PATCH] PCI/LINK: bw_notification: Do not leave interrupt handler NULL

[Alexandru Gagniuc]

A threaded IRQ with a NULL handler does not work with level-triggered
interrupts. request_threaded_irq() will return an error:

  genirq: Threaded irq requested with handler=NULL and !ONESHOT for irq 16
  pcie_bw_notification: probe of 0000:00:1b.0:pcie010 failed with error -22

For level interrupts we need to silence the interrupt before exiting
the IRQ handler, so just clear the PCI_EXP_LNKSTA_LBMS bit there.

Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Alexandru Gagniuc <mr.nuke...@gmail.com>
---

OOPS! I'm sorry for the noise. Here's the fix.

I was able to test this on edge-triggered interrupts. None of my
machines have PCIe ports that use level-triggered interrupts. This
might not be too straightforward to test without a hardware yanker,
but if there's a way to force a specific interrupt to be level
triggered, I could do the testing on my end.

 drivers/pci/pcie/bw_notification.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pcie/bw_notification.c 
b/drivers/pci/pcie/bw_notification.c
index d2eae3b7cc0f..001d6253ad48 100644
--- a/drivers/pci/pcie/bw_notification.c
+++ b/drivers/pci/pcie/bw_notification.c
@@ -44,11 +44,10 @@ static void pcie_disable_link_bandwidth_notification(struct 
pci_dev *dev)
        pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnk_ctl);
 }
 
-static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
+static irqreturn_t pcie_bw_notification_irq(int irq, void *context)
 {
        struct pcie_device *srv = context;
        struct pci_dev *port = srv->port;
-       struct pci_dev *dev;
        u16 link_status, events;
        int ret;
 
@@ -58,6 +57,17 @@ static irqreturn_t pcie_bw_notification_handler(int irq, 
void *context)
        if (ret != PCIBIOS_SUCCESSFUL || !events)
                return IRQ_NONE;
 
+       pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
+       return IRQ_WAKE_THREAD;
+}
+
+static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
+{
+       struct pcie_device *srv = context;
+       struct pci_dev *port = srv->port;
+       struct pci_dev *dev;
+       u16 link_status;
+
        /*
         * Print status from downstream devices, not this root port or
         * downstream switch port.
@@ -67,8 +77,8 @@ static irqreturn_t pcie_bw_notification_handler(int irq, void 
*context)
                __pcie_print_link_status(dev, false);
        up_read(&pci_bus_sem);
 
+       pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
        pcie_update_link_speed(port->subordinate, link_status);
-       pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
        return IRQ_HANDLED;
 }
 
@@ -80,7 +90,8 @@ static int pcie_bandwidth_notification_probe(struct 
pcie_device *srv)
        if (!pcie_link_bandwidth_notification_supported(srv->port))
                return -ENODEV;
 
-       ret = request_threaded_irq(srv->irq, NULL, pcie_bw_notification_handler,
+       ret = request_threaded_irq(srv->irq, pcie_bw_notification_irq,
+                                  pcie_bw_notification_handler,
                                   IRQF_SHARED, "PCIe BW notif", srv);
        if (ret)
                return ret;
-- 
2.19.2