Re: [PATCH v3 6/9] pci: Add slot and bus reset interfaces

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 2013-08-01 at 17:22 -0400, Don Dutile wrote:
> On 08/01/2013 12:55 PM, Alex Williamson wrote:
> > Sometimes pci_reset_function is not sufficient.  We have cases where
> > devices do not support any kind of reset, but there might be multiple
> > functions on the bus preventing pci_reset_function from doing a
> > secondary bus reset.  We also have cases where a device will advertise
> > that it supports a PM reset, but really does nothing on D3hot->D0
> > (graphics cards are notorious for this).  These devices often also
> > have more than one function, so even blacklisting PM reset for them
> > wouldn't allow a secondary bus reset through pci_reset_function.
> >
> > If a driver supports multiple devices it should have the ability to
> > induce a bus reset when it needs to.  This patch provides that ability
> > through pci_reset_slot and pci_reset_bus.  It's the caller's
> > responsibility when using these interfaces to understand that all of
> > the devices in or below the slot (or on or below the bus) will be
> > reset and therefore should be under control of the caller.  PCI state
> > of all the affected devices is saved and restored around these resets,
> > but internal state of all of the affected devices is reset (which
> > should be the intention).
> >
> > Signed-off-by: Alex Williamson<alex.williamson@redhat.com>
> > ---
> >   drivers/pci/pci.c   |  195 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >   include/linux/pci.h |    2 +
> >   2 files changed, 197 insertions(+)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index f6c757a..91f7bc4 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3518,6 +3518,201 @@ int pci_reset_function(struct pci_dev *dev)
> >   }
> >   EXPORT_SYMBOL_GPL(pci_reset_function);
> >
> > +static void pci_bus_lock(struct pci_bus *bus)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&bus->devices, bus_list) {
> > +		pci_dev_lock(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_lock(dev->subordinate);
> > +	}
> > +}
> > +
> > +static void pci_bus_unlock(struct pci_bus *bus)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&bus->devices, bus_list) {
> > +		pci_dev_unlock(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_unlock(dev->subordinate);
> > +	}
> > +}
> So, I'm wondering if the above locks from top of PCI tree down,
> should the unlock work from bottom back to the top ?
> i.e.,
> 	list_for_each_entry(dev,&bus->devices, bus_list) {
> 		if (dev->subordinate)
> 			pci_bus_unlock(dev->subordinate);
> 		pci_dev_unlock(dev);
> 	}


I hadn't considered that, it does seem like a good idea though.

> > +static void pci_slot_lock(struct pci_slot *slot)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&slot->bus->devices, bus_list) {
> > +		if (!dev->slot || dev->slot != slot)
> > +			continue;
> > +		pci_dev_lock(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_lock(dev->subordinate);
> > +	}
> > +}
> > +
> > +static void pci_slot_unlock(struct pci_slot *slot)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&slot->bus->devices, bus_list) {
> > +		if (!dev->slot || dev->slot != slot)
> > +			continue;
> > +		pci_dev_unlock(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_unlock(dev->subordinate);
> > +	}
> > +}
> ditto.
> 
> > +
> > +static void pci_bus_save_and_disable(struct pci_bus *bus)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&bus->devices, bus_list) {
> > +		pci_dev_save_and_disable(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_save_and_disable(dev->subordinate);
> > +	}
> > +}
> > +
> > +static void pci_bus_restore(struct pci_bus *bus)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&bus->devices, bus_list) {
> > +		pci_dev_restore(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_restore(dev->subordinate);
> > +	}
> > +}
> but not in reverse here, b/c need top-most device restored
> to get to next level in PCI tree (since could be a PPB that needs
> restoring to get to next level bus/device(s)).

Right.  Thanks, I'll see if there are any more comments and respin.

Alex

> > +
> > +static void pci_slot_save_and_disable(struct pci_slot *slot)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&slot->bus->devices, bus_list) {
> > +		if (!dev->slot || dev->slot != slot)
> > +			continue;
> > +		pci_dev_save_and_disable(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_save_and_disable(dev->subordinate);
> > +	}
> > +}
> > +
> > +static void pci_slot_restore(struct pci_slot *slot)
> > +{
> > +	struct pci_dev *dev;
> > +
> > +	list_for_each_entry(dev,&slot->bus->devices, bus_list) {
> > +		if (!dev->slot || dev->slot != slot)
> > +			continue;
> > +		pci_dev_restore(dev);
> > +		if (dev->subordinate)
> > +			pci_bus_restore(dev->subordinate);
> > +	}
> > +}
> ditto.
> 
> > +
> > +static int pci_slot_reset(struct pci_slot *slot, int probe)
> > +{
> > +	int rc;
> > +
> > +	if (!slot)
> > +		return -ENOTTY;
> > +
> > +	if (!probe)
> > +		pci_slot_lock(slot);
> > +
> > +	might_sleep();
> > +
> > +	rc = pci_reset_hotplug_slot(slot->hotplug, probe);
> > +
> > +	if (!probe)
> > +		pci_slot_unlock(slot);
> > +
> > +	return rc;
> > +}
> > +
> > +/**
> > + * pci_reset_slot - reset a PCI slot
> > + * @slot: PCI slot to reset
> > + *
> > + * A PCI bus may host multiple slots, each slot may support a reset mechanism
> > + * independent of other slots.  For instance, some slots may support slot power
> > + * control.  In the case of a 1:1 bus to slot architecture, this function may
> > + * wrap the bus reset to avoid spurious slot related events such as hotplug.
> > + * Generally a slot reset should be attempted before a bus reset.  All of the
> > + * function of the slot and any subordinate buses behind the slot are reset
> > + * through this function.  PCI config space of all devices in the slot and
> > + * behind the slot is saved before and restored after reset.
> > + *
> > + * Return 0 on success, non-zero on error.
> > + */
> > +int pci_reset_slot(struct pci_slot *slot)
> > +{
> > +	int rc;
> > +
> > +	rc = pci_slot_reset(slot, 1);
> > +	if (rc)
> > +		return rc;
> > +
> > +	pci_slot_save_and_disable(slot);
> > +
> > +	rc = pci_slot_reset(slot, 0);
> > +
> > +	pci_slot_restore(slot);
> > +
> > +	return rc;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_reset_slot);
> > +
> > +static int pci_bus_reset(struct pci_bus *bus, int probe)
> > +{
> > +	if (!bus->self)
> > +		return -ENOTTY;
> > +
> > +	if (probe)
> > +		return 0;
> > +
> > +	pci_bus_lock(bus);
> > +
> > +	might_sleep();
> > +
> > +	pci_reset_bridge_secondary_bus(bus->self);
> > +
> > +	pci_bus_unlock(bus);
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * pci_reset_bus - reset a PCI bus
> > + * @bus: top level PCI bus to reset
> > + *
> > + * Do a bus reset on the given bus and any subordinate buses, saving
> > + * and restoring state of all devices.
> > + *
> > + * Return 0 on success, non-zero on error.
> > + */
> > +int pci_reset_bus(struct pci_bus *bus)
> > +{
> > +	int rc;
> > +
> > +	rc = pci_bus_reset(bus, 1);
> > +	if (rc)
> > +		return rc;
> > +
> > +	pci_bus_save_and_disable(bus);
> > +
> > +	rc = pci_bus_reset(bus, 0);
> > +
> > +	pci_bus_restore(bus);
> > +
> > +	return rc;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_reset_bus);
> > +
> >   /**
> >    * pcix_get_max_mmrbc - get PCI-X maximum designed memory read byte count
> >    * @dev: PCI device to query
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 35c1bc4..1a8fd34 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -924,6 +924,8 @@ int pcie_set_mps(struct pci_dev *dev, int mps);
> >   int __pci_reset_function(struct pci_dev *dev);
> >   int __pci_reset_function_locked(struct pci_dev *dev);
> >   int pci_reset_function(struct pci_dev *dev);
> > +int pci_reset_slot(struct pci_slot *slot);
> > +int pci_reset_bus(struct pci_bus *bus);
> >   void pci_reset_bridge_secondary_bus(struct pci_dev *dev);
> >   void pci_update_resource(struct pci_dev *dev, int resno);
> >   int __must_check pci_assign_resource(struct pci_dev *dev, int i);
> >
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