PCI/MSI: Enable and mask MSI-X early

The ordering of MSI-X enable in hardware is dysfunctional:

 1) MSI-X is disabled in the control register
 2) Various setup functions
 3) pci_msi_setup_msi_irqs() is invoked which ends up accessing
    the MSI-X table entries
 4) MSI-X is enabled and masked in the control register with the
    comment that enabling is required for some hardware to access
    the MSI-X table

Step #4 obviously contradicts #3. The history of this is an issue with the
NIU hardware. When #4 was introduced the table access actually happened in
msix_program_entries() which was invoked after enabling and masking MSI-X.

This was changed in commit d71d6432e105 ("PCI/MSI: Kill redundant call of
irq_set_msi_desc() for MSI-X interrupts") which removed the table write
from msix_program_entries().

Interestingly enough nobody noticed and either NIU still works or it did
not get any testing with a kernel 3.19 or later.

Nevertheless this is inconsistent and there is no reason why MSI-X can't be
enabled and masked in the control register early on, i.e. move step #4
above to step #1. This preserves the NIU workaround and has no side effects
on other hardware.

Fixes: d71d6432e105 ("PCI/MSI: Kill redundant call of irq_set_msi_desc() for MSI-X interrupts")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210729222542.344136412@linutronix.de

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 9232255..5d39ed8 100644 (file)
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -772,18 +772,25 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
        u16 control;
        void __iomem *base;
 
-       /* Ensure MSI-X is disabled while it is set up */
-       pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);
+       /*
+        * Some devices require MSI-X to be enabled before the MSI-X
+        * registers can be accessed.  Mask all the vectors to prevent
+        * interrupts coming in before they're fully set up.
+        */
+       pci_msix_clear_and_set_ctrl(dev, 0, PCI_MSIX_FLAGS_MASKALL |
+                                   PCI_MSIX_FLAGS_ENABLE);
 
        pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
        /* Request & Map MSI-X table region */
        base = msix_map_region(dev, msix_table_size(control));
-       if (!base)
-               return -ENOMEM;
+       if (!base) {
+               ret = -ENOMEM;
+               goto out_disable;
+       }
 
        ret = msix_setup_entries(dev, base, entries, nvec, affd);
        if (ret)
-               return ret;
+               goto out_disable;
 
        ret = pci_msi_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
        if (ret)
@@ -794,14 +801,6 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
        if (ret)
                goto out_free;
 
-       /*
-        * Some devices require MSI-X to be enabled before we can touch the
-        * MSI-X registers.  We need to mask all the vectors to prevent
-        * interrupts coming in before they're fully set up.
-        */
-       pci_msix_clear_and_set_ctrl(dev, 0,
-                               PCI_MSIX_FLAGS_MASKALL | PCI_MSIX_FLAGS_ENABLE);
-
        msix_program_entries(dev, entries);
 
        ret = populate_msi_sysfs(dev);
@@ -836,6 +835,9 @@ out_avail:
 out_free:
        free_msi_irqs(dev);
 
+out_disable:
+       pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);
+
        return ret;
 }