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. This duplicates the code from the scan loop.
Furthermore the non ARI branch of next_fn() is generally hard to
understand and especially the check for multifunction devices is hidden
in the handling of NULL devices for non-contiguous multifunction. It
also signals that no further functions need to be scanned by returning
0 via wraparound and this is a valid function number.
Improve upon this by transforming the conditions in next_fn() to be
easier to understand.
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. This also makes it more explicit
that only function 0 must exist.
No functional change is intended.
Cc: Jan Kiszka <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
---
drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a969942d37..b05d0ed83a24 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2579,8 +2579,7 @@ 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;
@@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
if (pci_ari_enabled(bus)) {
if (!dev)
- return 0;
+ return -ENODEV;
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;
+ if (fn >= 7)
+ return -ENODEV;
+ /* only multifunction devices may have more functions */
+ if (dev && !dev->multifunction)
+ return -ENODEV;
- return 0;
+ return fn + 1;
}
static int only_one_child(struct pci_bus *bus)
@@ -2643,26 +2644,25 @@ 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 = 0, nr = 0;
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)) {
+ do {
dev = pci_scan_single_device(bus, devfn + fn);
if (dev) {
if (!pci_dev_is_added(dev))
nr++;
- dev->multifunction = 1;
+ if (fn > 0)
+ dev->multifunction = 1;
+ } else if (fn == 0) {
+ /* function 0 is required */
+ break;
}
- }
+ fn = next_fn(bus, dev, fn);
+ } while (fn >= 0);
/* Only one slot has PCIe device */
if (bus->self && nr)
--
2.32.0
On 6/28/22 16:30, 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. This duplicates the code from the scan loop.
>
> Furthermore the non ARI branch of next_fn() is generally hard to
> understand and especially the check for multifunction devices is hidden
> in the handling of NULL devices for non-contiguous multifunction. It
> also signals that no further functions need to be scanned by returning
> 0 via wraparound and this is a valid function number.
>
> Improve upon this by transforming the conditions in next_fn() to be
> easier to understand.
>
> 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. This also makes it more explicit
> that only function 0 must exist.
>
> No functional change is intended.
>
> Cc: Jan Kiszka <[email protected]>
> Signed-off-by: Niklas Schnelle <[email protected]>
> ---
> drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
> 1 file changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..b05d0ed83a24 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2579,8 +2579,7 @@ 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;
> @@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
>
> if (pci_ari_enabled(bus)) {
> if (!dev)
> - return 0;
> + return -ENODEV;
> 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;
> + if (fn >= 7)
> + return -ENODEV;
> + /* only multifunction devices may have more functions */
> + if (dev && !dev->multifunction)
> + return -ENODEV;
>
> - return 0;
> + return fn + 1;
No more % 8 ?
Even it disapear later shouldn't we keep it ?
> }
>
> static int only_one_child(struct pci_bus *bus)
> @@ -2643,26 +2644,25 @@ 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 = 0, nr = 0;
>
> 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)) {
> + do {
> dev = pci_scan_single_device(bus, devfn + fn);
> if (dev) {
> if (!pci_dev_is_added(dev))
> nr++;
> - dev->multifunction = 1;
> + if (fn > 0)
> + dev->multifunction = 1;
> + } else if (fn == 0) {
> + /* function 0 is required */
> + break;
> }
> - }
> + fn = next_fn(bus, dev, fn);
> + } while (fn >= 0);
>
> /* Only one slot has PCIe device */
> if (bus->self && nr)
>
Otherwise LGTM
--
Pierre Morel
IBM Lab Boeblingen
On Thu, 2022-06-30 at 14:40 +0200, Pierre Morel wrote:
>
> On 6/28/22 16:30, 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. This duplicates the code from the scan loop.
> >
> > Furthermore the non ARI branch of next_fn() is generally hard to
> > understand and especially the check for multifunction devices is hidden
> > in the handling of NULL devices for non-contiguous multifunction. It
> > also signals that no further functions need to be scanned by returning
> > 0 via wraparound and this is a valid function number.
> >
> > Improve upon this by transforming the conditions in next_fn() to be
> > easier to understand.
> >
> > 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. This also makes it more explicit
> > that only function 0 must exist.
> >
> > No functional change is intended.
> >
> > Cc: Jan Kiszka <[email protected]>
> > Signed-off-by: Niklas Schnelle <[email protected]>
> > ---
> > drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
> > 1 file changed, 19 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 17a969942d37..b05d0ed83a24 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -2579,8 +2579,7 @@ 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;
> > @@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
> >
> > if (pci_ari_enabled(bus)) {
> > if (!dev)
> > - return 0;
> > + return -ENODEV;
> > 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;
> > + if (fn >= 7)
> > + return -ENODEV;
> > + /* only multifunction devices may have more functions */
> > + if (dev && !dev->multifunction)
> > + return -ENODEV;
> >
> > - return 0;
> > + return fn + 1;
>
> No more % 8 ?
> Even it disapear later shouldn't we keep it ?
The "% 8" became unnecessary due to the explicit "if (fn >= 7)"
above.
The original "% 8" did what I referred to in the commit message with
"It [the function] also signals that no further functions need to be
scanned by returning 0 via wraparound and this is a valid function
number.". Instead we now explicitly return -ENODEV in this case.
>
>
>
> > }
> >
> > static int only_one_child(struct pci_bus *bus)
> > @@ -2643,26 +2644,25 @@ 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 = 0, nr = 0;
> >
> > 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)) {
> > + do {
> > dev = pci_scan_single_device(bus, devfn + fn);
> > if (dev) {
> > if (!pci_dev_is_added(dev))
> > nr++;
> > - dev->multifunction = 1;
> > + if (fn > 0)
> > + dev->multifunction = 1;
> > + } else if (fn == 0) {
> > + /* function 0 is required */
> > + break;
> > }
> > - }
> > + fn = next_fn(bus, dev, fn);
> > + } while (fn >= 0);
> >
> > /* Only one slot has PCIe device */
> > if (bus->self && nr)
> >
>
> Otherwise LGTM
>
Thanks for taking a look!
On 6/30/22 15:48, Niklas Schnelle wrote:
> On Thu, 2022-06-30 at 14:40 +0200, Pierre Morel wrote:
>>
>> On 6/28/22 16:30, 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. This duplicates the code from the scan loop.
>>>
>>> Furthermore the non ARI branch of next_fn() is generally hard to
>>> understand and especially the check for multifunction devices is hidden
>>> in the handling of NULL devices for non-contiguous multifunction. It
>>> also signals that no further functions need to be scanned by returning
>>> 0 via wraparound and this is a valid function number.
>>>
>>> Improve upon this by transforming the conditions in next_fn() to be
>>> easier to understand.
>>>
>>> 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. This also makes it more explicit
>>> that only function 0 must exist.
>>>
>>> No functional change is intended.
>>>
>>> Cc: Jan Kiszka <[email protected]>
>>> Signed-off-by: Niklas Schnelle <[email protected]>
>>> ---
>>> drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
>>> 1 file changed, 19 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>>> index 17a969942d37..b05d0ed83a24 100644
>>> --- a/drivers/pci/probe.c
>>> +++ b/drivers/pci/probe.c
>>> @@ -2579,8 +2579,7 @@ 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;
>>> @@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
>>>
>>> if (pci_ari_enabled(bus)) {
>>> if (!dev)
>>> - return 0;
>>> + return -ENODEV;
>>> 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;
>>> + if (fn >= 7)
>>> + return -ENODEV;
>>> + /* only multifunction devices may have more functions */
>>> + if (dev && !dev->multifunction)
>>> + return -ENODEV;
>>>
>>> - return 0;
>>> + return fn + 1;
>>
>> No more % 8 ?
>> Even it disapear later shouldn't we keep it ?
>
> The "% 8" became unnecessary due to the explicit "if (fn >= 7)"
> above.
> The original "% 8" did what I referred to in the commit message with
> "It [the function] also signals that no further functions need to be
> scanned by returning 0 via wraparound and this is a valid function
> number.". Instead we now explicitly return -ENODEV in this case.
Yes it goes with it.
With this code next_fn returns -ENODEV for fn = 8 instead of previously
returning 1. (If I am right)
With the previous code, did we assume that next_fn is never called with
fn > 7?
I guess yes as we test pci_ari_enabled first and without ARI we do not
have more than 7 more functions. is it right?
For what I think this new code seems better as it does not make the
assumption that it get called with fn < 8.
>
>>
>>
>>
>>> }
>>>
>>> static int only_one_child(struct pci_bus *bus)
>>> @@ -2643,26 +2644,25 @@ 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 = 0, nr = 0;
>>>
>>> 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)) {
>>> + do {
>>> dev = pci_scan_single_device(bus, devfn + fn);
>>> if (dev) {
>>> if (!pci_dev_is_added(dev))
>>> nr++;
>>> - dev->multifunction = 1;
>>> + if (fn > 0)
>>> + dev->multifunction = 1;
>>> + } else if (fn == 0) {
>>> + /* function 0 is required */
>>> + break;
>>> }
>>> - }
>>> + fn = next_fn(bus, dev, fn);
>>> + } while (fn >= 0);
>>>
>>> /* Only one slot has PCIe device */
>>> if (bus->self && nr)
>>>
>>
>> Otherwise LGTM
>>
>
> Thanks for taking a look!
>
--
Pierre Morel
IBM Lab Boeblingen
On Thu, 2022-06-30 at 16:50 +0200, Pierre Morel wrote:
> > >
>
> On 6/30/22 15:48, Niklas Schnelle wrote:
> > On Thu, 2022-06-30 at 14:40 +0200, Pierre Morel wrote:
> > > On 6/28/22 16:30, 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. This duplicates the code from the scan loop.
> > > >
> > > > Furthermore the non ARI branch of next_fn() is generally hard to
> > > > understand and especially the check for multifunction devices is hidden
> > > > in the handling of NULL devices for non-contiguous multifunction. It
> > > > also signals that no further functions need to be scanned by returning
> > > > 0 via wraparound and this is a valid function number.
> > > >
> > > > Improve upon this by transforming the conditions in next_fn() to be
> > > > easier to understand.
> > > >
> > > > 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. This also makes it more explicit
> > > > that only function 0 must exist.
> > > >
> > > > No functional change is intended.
> > > >
> > > > Cc: Jan Kiszka <[email protected]>
> > > > Signed-off-by: Niklas Schnelle <[email protected]>
> > > > ---
> > > > drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
> > > > 1 file changed, 19 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > > > index 17a969942d37..b05d0ed83a24 100644
> > > > --- a/drivers/pci/probe.c
> > > > +++ b/drivers/pci/probe.c
> > > > @@ -2579,8 +2579,7 @@ 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;
> > > > @@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
> > > >
> > > > if (pci_ari_enabled(bus)) {
> > > > if (!dev)
> > > > - return 0;
> > > > + return -ENODEV;
> > > > 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;
> > > > + if (fn >= 7)
> > > > + return -ENODEV;
> > > > + /* only multifunction devices may have more functions */
> > > > + if (dev && !dev->multifunction)
> > > > + return -ENODEV;
> > > >
> > > > - return 0;
> > > > + return fn + 1;
> > >
> > > No more % 8 ?
> > > Even it disapear later shouldn't we keep it ?
> >
> > The "% 8" became unnecessary due to the explicit "if (fn >= 7)"
> > above.
> > The original "% 8" did what I referred to in the commit message with
> > "It [the function] also signals that no further functions need to be
> > scanned by returning 0 via wraparound and this is a valid function
> > number.". Instead we now explicitly return -ENODEV in this case.
>
> Yes it goes with it.
> With this code next_fn returns -ENODEV for fn = 8 instead of previously
> returning 1. (If I am right)
>
> With the previous code, did we assume that next_fn is never called with
> fn > 7?
> I guess yes as we test pci_ari_enabled first and without ARI we do not
> have more than 7 more functions. is it right?
>
> For what I think this new code seems better as it does not make the
> assumption that it get called with fn < 8.
>
The fn value in this case iterates through the least significant 3 bits
of the geographical PCI address so yes this limits it to 7 functions.
My main qualm with the old code was that returning 0 for the end is
ambiguous because that is also a valid devfn.