[PATCH v2] PCI: Restore the original INTX_DISABLE bit by pcim_intx()

[Takashi Iwai <tiwai@xxxxxxx>]

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.

Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")
Cc: stable@xxxxxxxxxxxxxxx # 6.11+
Link: https://lore.kernel.org/87v7xk2ps5.wl-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
v1->v2: refactoring, fold get_or_create_intx_devres() into the caller
instead of retrieving the original INTx there.
Also add comments and improve the patch description.

 drivers/pci/devres.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c
index b133967faef8..c93d4d4499a0 100644
--- a/drivers/pci/devres.c
+++ b/drivers/pci/devres.c
@@ -438,19 +438,12 @@ static void pcim_intx_restore(struct device *dev, void *data)
 	__pcim_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;
+	u16 pci_command;
 
-	res = devres_find(dev, pcim_intx_restore, NULL, NULL);
-	if (res)
-		return res;
-
-	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);
 }
 
 /**
@@ -466,12 +459,23 @@ 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;
 	__pcim_intx(pdev, enable);
 
 	return 0;
-- 
2.43.0