diff mbox series

[v2,1/4] PCI: Clean up pci_scan_slot()

Message ID 20220412143040.1882096-2-schnelle@linux.ibm.com (mailing list archive)
State Superseded
Headers show
Series PCI: Rework pci_scan_slot() and isolated PCI functions | expand

Commit Message

Niklas Schnelle April 12, 2022, 2:30 p.m. UTC 
While determining the next PCI function is factored out of
pci_scan_slot() into next_fn() the former still handles the first
function as a special case duplicating the code from the scan loop and
splitting the condition that the first function exits from it being
multifunction which is tested in next_fn().

Furthermore the non ARI branch of next_fn() mixes the case that
multifunction devices may have non-contiguous function ranges and dev
may thus be NULL with the multifunction requirement. It also signals
that no further functions need to be scanned by returning 0 which is
a valid function number.

Improve upon this by moving all conditions for having to scan for more
functions into next_fn() and make them obvious and commented.

By changing next_fn() to return -ENODEV instead of 0 when there is no
next function we can then handle the initial function inside the loop
and deduplicate the shared handling.

No functional change is intended.

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 drivers/pci/probe.c | 41 +++++++++++++++++++----------------------
 1 file changed, 19 insertions(+), 22 deletions(-)

Comments

Niklas Schnelle April 12, 2022, 3:24 p.m. UTC | #1 
On Tue, 2022-04-12 at 16:30 +0200, Niklas Schnelle wrote:
> While determining the next PCI function is factored out of
> pci_scan_slot() into next_fn() the former still handles the first
> function as a special case duplicating the code from the scan loop and
> splitting the condition that the first function exits from it being
> multifunction which is tested in next_fn().
> 
> Furthermore the non ARI branch of next_fn() mixes the case that
> multifunction devices may have non-contiguous function ranges and dev
> may thus be NULL with the multifunction requirement. It also signals
> that no further functions need to be scanned by returning 0 which is
> a valid function number.
> 
> Improve upon this by moving all conditions for having to scan for more
> functions into next_fn() and make them obvious and commented.
> 
> By changing next_fn() to return -ENODEV instead of 0 when there is no
> next function we can then handle the initial function inside the loop
> and deduplicate the shared handling.
> 
> No functional change is intended.
> 
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
>  drivers/pci/probe.c | 41 +++++++++++++++++++----------------------
>  1 file changed, 19 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..389aa1f9cb2c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2579,33 +2579,35 @@ struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
>  }
>  EXPORT_SYMBOL(pci_scan_single_device);
>  
> -static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
> -			    unsigned int fn)
> +static int next_fn(struct pci_bus *bus, struct pci_dev *dev, int fn)
>  {
>  	int pos;
>  	u16 cap = 0;
>  	unsigned int next_fn;
>  
> -	if (pci_ari_enabled(bus)) {
> -		if (!dev)
> -			return 0;

This part here theoretically changes the behavior slightly. If the ARI
information is wrong/lands us in a "hole" we may look for more
functions via the non-ARI path. Not sure if that is relevant though as
in the worst case we might find functions that we otherwise wouldn't
have seen. Seems rather obsure to me but I might be wrong, we currently
don't see the ARI capability in Linux on IBM Z so I have less
experience with this. I did of course boot test on my x86_64
workstation.

> +	if (dev && pci_ari_enabled(bus)) {
>  		pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI);
>  		if (!pos)
> -			return 0;
> +			return -ENODEV;
>  
>  		pci_read_config_word(dev, pos + PCI_ARI_CAP, &cap);
>  		next_fn = PCI_ARI_CAP_NFN(cap);
>  		if (next_fn <= fn)
> -			return 0;	/* protect against malformed list */
> +			return -ENODEV;	/* protect against malformed list */
>  
>  		return next_fn;
>  	}
>  
> -	/* dev may be NULL for non-contiguous multifunction devices */
> -	if (!dev || dev->multifunction)
> -		return (fn + 1) % 8;
> -
> -	return 0;
> +	/* only multifunction devices may have more functions */
> +	if (dev && !dev->multifunction)
> +		return -ENODEV;
> +	/*
> +	 * A function 0 is required but multifunction devices may
> +	 * be non-contiguous so dev can be NULL otherwise.
> +	 */
> +	if (!fn && !dev)
> +		return -ENODEV;
> +	return (fn <= 6) ? fn + 1 : -ENODEV;
>  }
>  
> 
---8<---
diff mbox series

Patch

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a969942d37..389aa1f9cb2c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2579,33 +2579,35 @@  struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
 }
 EXPORT_SYMBOL(pci_scan_single_device);
 
-static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
-			    unsigned int fn)
+static int next_fn(struct pci_bus *bus, struct pci_dev *dev, int fn)
 {
 	int pos;
 	u16 cap = 0;
 	unsigned int next_fn;
 
-	if (pci_ari_enabled(bus)) {
-		if (!dev)
-			return 0;
+	if (dev && pci_ari_enabled(bus)) {
 		pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI);
 		if (!pos)
-			return 0;
+			return -ENODEV;
 
 		pci_read_config_word(dev, pos + PCI_ARI_CAP, &cap);
 		next_fn = PCI_ARI_CAP_NFN(cap);
 		if (next_fn <= fn)
-			return 0;	/* protect against malformed list */
+			return -ENODEV;	/* protect against malformed list */
 
 		return next_fn;
 	}
 
-	/* dev may be NULL for non-contiguous multifunction devices */
-	if (!dev || dev->multifunction)
-		return (fn + 1) % 8;
-
-	return 0;
+	/* only multifunction devices may have more functions */
+	if (dev && !dev->multifunction)
+		return -ENODEV;
+	/*
+	 * A function 0 is required but multifunction devices may
+	 * be non-contiguous so dev can be NULL otherwise.
+	 */
+	if (!fn && !dev)
+		return -ENODEV;
+	return (fn <= 6) ? fn + 1 : -ENODEV;
 }
 
 static int only_one_child(struct pci_bus *bus)
@@ -2643,24 +2645,19 @@  static int only_one_child(struct pci_bus *bus)
  */
 int pci_scan_slot(struct pci_bus *bus, int devfn)
 {
-	unsigned int fn, nr = 0;
-	struct pci_dev *dev;
+	int fn, nr = 0;
+	struct pci_dev *dev = NULL;
 
 	if (only_one_child(bus) && (devfn > 0))
 		return 0; /* Already scanned the entire slot */
 
-	dev = pci_scan_single_device(bus, devfn);
-	if (!dev)
-		return 0;
-	if (!pci_dev_is_added(dev))
-		nr++;
-
-	for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) {
+	for (fn = 0; fn >= 0; fn = next_fn(bus, dev, fn)) {
 		dev = pci_scan_single_device(bus, devfn + fn);
 		if (dev) {
 			if (!pci_dev_is_added(dev))
 				nr++;
-			dev->multifunction = 1;
+			if (nr > 1)
+				dev->multifunction = 1;
 		}
 	}