On 06/18/2013 04:06 AM, Bjorn Helgaas wrote:
> On Sun, May 26, 2013 at 11:52:58PM +0800, Jiang Liu wrote:
>> Introduce hotplug-safe PCI bus iterators as below, which hold a
>> reference on the returned PCI bus object.
>> bool pci_bus_exists(int domain, int busnr);
>> struct pci_bus *pci_get_bus(int domain, int busnr);
>> struct pci_bus *pci_get_next_bus(struct pci_bus *from);
>> struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
>> #define for_each_pci_bus(b) for (b = NULL; (b = pci_get_next_bus(b)); )
>> #define for_each_pci_root_bus(b) \
>> for (b = NULL; (b = pci_get_next_root_bus(b)); )
>>
>> The long-term goal is to remove hotplug-unsafe pci_find_bus(),
>> pci_find_next_bus() and the global pci_root_buses list.
>
> I think you should mark the unsafe interfaces as __deprecated so
> users will get compile-time warnings.
>
> I don't think pci_bus_exists() is a safe interface, because the value
> it returns may be incorrect before the caller can look at it. The
> only safe thing would be to make it so we try to create the bus
> and return failure if it already exists. Then the mutex can be in
> the code that creates the bus.
>
> I don't see any uses of for_each_pci_bus(), so please remove that.
>
> It sounds like we don't have a consensus on how to iterate over
> PCI root buses. If you separate that from the pci_get_bus()
> changes, maybe we can at least move forward on the pci_get_bus()
> stuff.
Hi Bjorn and Yinghai,
I have thought about the way to implement pci_for_each_root_bus()
again. And there are several possible ways here:
1) Yinghai has a patch set implementing an iterator for PCI host
bridges, but we can't safely refer the PCI root bus associated with a
host bridge device because the host bridge doesn't hold a reference to
associated PCI root bus. So we need to find a safe way to refer the PCI
root bus associated with a PCI host bridge.
2) Unexport pci_root_buses and convert it to klist, then we could walk
all root buses effectively. This solution is straight-forward, but it
may break out of tree drivers.
3) Keep current implementation, which does waste some computation cycles:(
So what's your thoughts about above solutions? Or any other suggestions?
Regards!
Gerry
>
> Bjorn
>
>> These new interfaces may be a littler slower than existing interfaces,
>> but it should be acceptable because they are not used on hot paths.
>>
>> Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxx>
>> Acked-by: Yinghai Lu <yinghai@xxxxxxxxxx>
>> Cc: linux-pci@xxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> ---
>> drivers/pci/pci.h | 1 +
>> drivers/pci/probe.c | 2 +-
>> drivers/pci/search.c | 159 +++++++++++++++++++++++++++++++++++++++++----------
>> include/linux/pci.h | 23 +++++++-
>> 4 files changed, 153 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index 68678ed..8fe15f6 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -126,6 +126,7 @@ static inline void pci_remove_legacy_files(struct pci_bus *bus) { return; }
>>
>> /* Lock for read/write access to pci device and bus lists */
>> extern struct rw_semaphore pci_bus_sem;
>> +extern struct class pcibus_class;
>>
>> extern raw_spinlock_t pci_lock;
>>
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 2830070..1004a05 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -93,7 +93,7 @@ static void release_pcibus_dev(struct device *dev)
>> kfree(pci_bus);
>> }
>>
>> -static struct class pcibus_class = {
>> +struct class pcibus_class = {
>> .name = "pci_bus",
>> .dev_release = &release_pcibus_dev,
>> .dev_attrs = pcibus_dev_attrs,
>> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
>> index d0627fa..16ccaf8 100644
>> --- a/drivers/pci/search.c
>> +++ b/drivers/pci/search.c
>> @@ -52,20 +52,27 @@ pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
>> return tmp;
>> }
>>
>> -static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
>> +struct pci_bus_match_arg {
>> + int domain;
>> + int bus;
>> +};
>> +
>> +static int pci_match_bus(struct device *dev, const void *data)
>> {
>> - struct pci_bus* child;
>> - struct list_head *tmp;
>> + struct pci_bus *bus = to_pci_bus(dev);
>> + const struct pci_bus_match_arg *arg = data;
>>
>> - if(bus->number == busnr)
>> - return bus;
>> + return (pci_domain_nr(bus) == arg->domain && bus->number == arg->bus);
>> +}
>>
>> - list_for_each(tmp, &bus->children) {
>> - child = pci_do_find_bus(pci_bus_b(tmp), busnr);
>> - if(child)
>> - return child;
>> - }
>> - return NULL;
>> +static int pci_match_next_bus(struct device *dev, const void *data)
>> +{
>> + return 1;
>> +}
>> +
>> +static int pci_match_next_root_bus(struct device *dev, const void *data)
>> +{
>> + return pci_is_root_bus(to_pci_bus(dev));
>> }
>>
>> /**
>> @@ -76,20 +83,19 @@ static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
>> * Given a PCI bus number and domain number, the desired PCI bus is located
>> * in the global list of PCI buses. If the bus is found, a pointer to its
>> * data structure is returned. If no bus is found, %NULL is returned.
>> + *
>> + * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
>> + * Please use pci_get_bus() instead which holds a reference on the returned
>> + * PCI bus.
>> */
>> -struct pci_bus * pci_find_bus(int domain, int busnr)
>> +struct pci_bus *pci_find_bus(int domain, int busnr)
>> {
>> - struct pci_bus *bus = NULL;
>> - struct pci_bus *tmp_bus;
>> + struct pci_bus *bus;
>>
>> - while ((bus = pci_find_next_bus(bus)) != NULL) {
>> - if (pci_domain_nr(bus) != domain)
>> - continue;
>> - tmp_bus = pci_do_find_bus(bus, busnr);
>> - if (tmp_bus)
>> - return tmp_bus;
>> - }
>> - return NULL;
>> + bus = pci_get_bus(domain, busnr);
>> + pci_bus_put(bus);
>> +
>> + return bus;
>> }
>>
>> /**
>> @@ -100,21 +106,114 @@ struct pci_bus * pci_find_bus(int domain, int busnr)
>> * initiated by passing %NULL as the @from argument. Otherwise if
>> * @from is not %NULL, searches continue from next device on the
>> * global list.
>> + *
>> + * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
>> + * Please use pci_get_next_root_bus() instead which holds a reference
>> + * on the returned PCI root bus.
>> */
>> struct pci_bus *
>> pci_find_next_bus(const struct pci_bus *from)
>> {
>> - struct list_head *n;
>> - struct pci_bus *b = NULL;
>> + struct device *dev = from ? (struct device *)&from->dev : NULL;
>> +
>> + dev = class_find_device(&pcibus_class, dev, NULL,
>> + &pci_match_next_root_bus);
>> + if (dev) {
>> + put_device(dev);
>> + return to_pci_bus(dev);
>> + }
>> +
>> + return NULL;
>> +}
>> +
>> +bool pci_bus_exists(int domain, int busnr)
>> +{
>> + struct device *dev;
>> + struct pci_bus_match_arg arg = { domain, busnr };
>>
>> WARN_ON(in_interrupt());
>> - down_read(&pci_bus_sem);
>> - n = from ? from->node.next : pci_root_buses.next;
>> - if (n != &pci_root_buses)
>> - b = pci_bus_b(n);
>> - up_read(&pci_bus_sem);
>> - return b;
>> + dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
>> + if (dev)
>> + put_device(dev);
>> +
>> + return dev != NULL;
>> +}
>> +EXPORT_SYMBOL(pci_bus_exists);
>> +
>> +/**
>> + * pci_get_bus - locate PCI bus from a given domain and bus number
>> + * @domain: number of PCI domain to search
>> + * @busnr: number of desired PCI bus
>> + *
>> + * Given a PCI bus number and domain number, the desired PCI bus is located.
>> + * If the bus is found, a pointer to its data structure is returned.
>> + * If no bus is found, %NULL is returned.
>> + * Caller needs to release the returned bus by calling pci_bus_put().
>> + */
>> +struct pci_bus *pci_get_bus(int domain, int busnr)
>> +{
>> + struct device *dev;
>> + struct pci_bus_match_arg arg = { domain, busnr };
>> +
>> + WARN_ON(in_interrupt());
>> + dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
>> + if (dev)
>> + return to_pci_bus(dev);
>> +
>> + return NULL;
>> +}
>> +EXPORT_SYMBOL(pci_get_bus);
>> +
>> +/**
>> + * pci_get_next_bus - begin or continue searching for a PCI bus
>> + * @from: Previous PCI bus found, or %NULL for new search.
>> + *
>> + * Iterates through the list of known PCI busses. If a PCI bus is found,
>> + * the reference count to the bus is incremented and a pointer to it is
>> + * returned. Otherwise, %NULL is returned. A new search is initiated by
>> + * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
>> + * searches continue from next bus on the global list. The reference count
>> + * for @from is always decremented if it is not %NULL.
>> + */
>> +struct pci_bus *pci_get_next_bus(struct pci_bus *from)
>> +{
>> + struct device *dev = from ? &from->dev : NULL;
>> +
>> + WARN_ON(in_interrupt());
>> + dev = class_find_device(&pcibus_class, dev, NULL, &pci_match_next_bus);
>> + pci_bus_put(from);
>> + if (dev)
>> + return to_pci_bus(dev);
>> +
>> + return NULL;
>> +}
>> +EXPORT_SYMBOL(pci_get_next_bus);
>> +
>> +/**
>> + * pci_find_next_root_bus - begin or continue searching for a PCI root bus
>> + * @from: Previous PCI bus found, or %NULL for new search.
>> + *
>> + * Iterates through the list of known PCI root busses. If a PCI bus is found,
>> + * the reference count to the root bus is incremented and a pointer to it is
>> + * returned. Otherwise, %NULL is returned. A new search is initiated by
>> + * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
>> + * searches continue from next root bus on the global list. The reference
>> + * count for @from is always decremented if it is not %NULL.
>> + */
>> +struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
>> +{
>> + struct device *dev = from ? &from->dev : NULL;
>> +
>> + WARN_ON(in_interrupt());
>> + dev = class_find_device(&pcibus_class, dev, NULL,
>> + &pci_match_next_root_bus);
>> + pci_bus_put(from);
>> + if (dev)
>> + return to_pci_bus(dev);
>> +
>> + return NULL;
>> }
>> +EXPORT_SYMBOL(pci_get_next_root_bus);
>>
>> /**
>> * pci_get_slot - locate PCI device for a given PCI slot
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 7b23fa0..1e43423 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -454,6 +454,9 @@ struct pci_bus {
>>
>> #define pci_bus_b(n) list_entry(n, struct pci_bus, node)
>> #define to_pci_bus(n) container_of(n, struct pci_bus, dev)
>> +#define for_each_pci_bus(b) for (b = NULL; (b = pci_get_next_bus(b)); )
>> +#define for_each_pci_root_bus(b) \
>> + for (b = NULL; (b = pci_get_next_root_bus(b)); )
>>
>> /*
>> * Returns true if the pci bus is root (behind host-pci bridge),
>> @@ -718,7 +721,6 @@ void pcibios_resource_to_bus(struct pci_dev *dev, struct pci_bus_region *region,
>> void pcibios_bus_to_resource(struct pci_dev *dev, struct resource *res,
>> struct pci_bus_region *region);
>> void pcibios_scan_specific_bus(int busn);
>> -struct pci_bus *pci_find_bus(int domain, int busnr);
>> void pci_bus_add_devices(const struct pci_bus *bus);
>> struct pci_bus * __deprecated pci_scan_bus_parented(struct device *parent,
>> int bus, struct pci_ops *ops, void *sysdata);
>> @@ -778,8 +780,15 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap);
>> int pci_find_next_ext_capability(struct pci_dev *dev, int pos, int cap);
>> int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
>> int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
>> +
>> +struct pci_bus *pci_find_bus(int domain, int busnr);
>> struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
>>
>> +bool pci_bus_exists(int domain, int busnr);
>> +struct pci_bus *pci_get_bus(int domain, int busnr);
>> +struct pci_bus *pci_get_next_bus(struct pci_bus *from);
>> +struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
>> +
>> struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
>> struct pci_dev *from);
>> struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
>> @@ -1430,6 +1439,18 @@ static inline void pci_unblock_cfg_access(struct pci_dev *dev)
>> static inline struct pci_bus *pci_find_next_bus(const struct pci_bus *from)
>> { return NULL; }
>>
>> +static inline bool pci_bus_exists(int domain, int busnr)
>> +{ return false; }
>> +
>> +static inline struct pci_bus *pci_get_bus(int domain, int busnr)
>> +{ return NULL; }
>> +
>> +static inline struct pci_bus *pci_get_next_bus(struct pci_bus *from)
>> +{ return NULL; }
>> +
>> +static inline struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
>> +{ return NULL; }
>> +
>> static inline struct pci_dev *pci_get_slot(struct pci_bus *bus,
>> unsigned int devfn)
>> { return NULL; }
>> --
>> 1.8.1.2
>>
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