PCI: Restore original INTX_DISABLE bit by pcim_intx()

pcim_intx() tries to restore the INTx bit at removal via devres, but there
is a chance that it restores a wrong value.

Because the value to be restored is blindly assumed to be the negative of
the enable argument, when a driver calls pcim_intx() unnecessarily for the
already enabled state, it'll restore to the disabled state in turn.  That
is, the function assumes the case like:

  // INTx == 1
  pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> correct

but it might be like the following, too:

  // INTx == 0
  pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> wrong

Also, when a driver calls pcim_intx() multiple times with different enable
argument values, the last one will win no matter what value it is.  This
can lead to inconsistency, e.g.

  // INTx == 1
  pcim_intx(pdev, 0); // OK
  ...
  pcim_intx(pdev, 1); // now old INTx wrongly assumed to be 0

This patch addresses those inconsistencies by saving the original INTx
state at the first pcim_intx() call.  For that, get_or_create_intx_devres()
is folded into pcim_intx() caller side; it allows us to simply check the
already allocated devres and record the original INTx along with the
devres_alloc() call.

Link: https://lore.kernel.org/r/20241031134300.10296-1-tiwai@suse.de
Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")
Link: https://lore.kernel.org/87v7xk2ps5.wl-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Philipp Stanner <pstanner@redhat.com>
Cc: stable@vger.kernel.org	# v6.11+

diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c
index d1d97a4bb36d38af260ef485b7e765cedd6813da..3431a7df3e0d9a196f9457a23aa73d82bd3e71b4 100644 (file)
--- a/drivers/pci/devres.c
+++ b/drivers/pci/devres.c
@@ -419,19 +419,12 @@ static void pcim_intx_restore(struct device *dev, void *data)
        pci_intx(pdev, res->orig_intx);
 }
 
-static struct pcim_intx_devres *get_or_create_intx_devres(struct device *dev)
+static void save_orig_intx(struct pci_dev *pdev, struct pcim_intx_devres *res)
 {
-       struct pcim_intx_devres *res;
-
-       res = devres_find(dev, pcim_intx_restore, NULL, NULL);
-       if (res)
-               return res;
+       u16 pci_command;
 
-       res = devres_alloc(pcim_intx_restore, sizeof(*res), GFP_KERNEL);
-       if (res)
-               devres_add(dev, res);
-
-       return res;
+       pci_read_config_word(pdev, PCI_COMMAND, &pci_command);
+       res->orig_intx = !(pci_command & PCI_COMMAND_INTX_DISABLE);
 }
 
 /**
@@ -447,12 +440,23 @@ static struct pcim_intx_devres *get_or_create_intx_devres(struct device *dev)
 int pcim_intx(struct pci_dev *pdev, int enable)
 {
        struct pcim_intx_devres *res;
+       struct device *dev = &pdev->dev;
 
-       res = get_or_create_intx_devres(&pdev->dev);
-       if (!res)
-               return -ENOMEM;
+       /*
+        * pcim_intx() must only restore the INTx value that existed before the
+        * driver was loaded, i.e., before it called pcim_intx() for the
+        * first time.
+        */
+       res = devres_find(dev, pcim_intx_restore, NULL, NULL);
+       if (!res) {
+               res = devres_alloc(pcim_intx_restore, sizeof(*res), GFP_KERNEL);
+               if (!res)
+                       return -ENOMEM;
+
+               save_orig_intx(pdev, res);
+               devres_add(dev, res);
+       }
 
-       res->orig_intx = !enable;
        pci_intx(pdev, enable);
 
        return 0;