Re: [PATCH v6 1/4] PCI: Consider alignment of hot-added bridges when distributing available resources

Nicholas Johnson
2019-06-19T13:47:10Z

Again, I am re-sending my previous response with reply-all instead of
plain reply. Mika, you can ignore this as you have already seen it. For
everybody else, everything below the line should be exactly the same as
I copied it over.
_______________________________________________________________________________

On Mon, Jun 17, 2019 at 12:35:13PM +0300, mika.westerberg@linux.intel.com wrote:
> On Wed, May 22, 2019 at 02:30:44PM +0000, Nicholas Johnson wrote:
> > Rewrite pci_bus_distribute_available_resources to better handle bridges
> > with different resource alignment requirements. Pass more details
> > arguments recursively to track the resource start and end addresses
> > relative to the initial hotplug bridge. This is especially useful for
> > Thunderbolt with native PCI enumeration, enabling external graphics
> > cards and other devices with bridge alignment higher than 0x100000
>
> Instead of 0x100000 you could say 1MB here.
My train of thought is 1MB is sometimes means base-10 but then again,
that is probably outside of the kernel world. I can change it to 1MB.

>
> > bytes.
> >
> > Change extend_bridge_window to resize the actual resource, rather than
> > using add_list and dev_res->add_size. If an additional resource entry
> > exists for the given resource, zero out the add_size field to avoid it
> > interfering. Because add_size is considered optional when allocating,
> > using add_size could cause issues in some cases, because successful
> > resource distribution requires sizes to be guaranteed. Such cases
> > include hot-adding nested hotplug bridges in one enumeration, and
> > potentially others which are yet to be encountered.
> >
> > Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
>
> The logic makes sense to me but since you probably need to spin another
> revision anyway please find a couple of additional comments below.
>
> > ---
> > drivers/pci/setup-bus.c | 169 ++++++++++++++++++++--------------------
> > 1 file changed, 84 insertions(+), 85 deletions(-)
> >
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index 0cdd5ff38..1b5b851ca 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -1835,12 +1835,10 @@ static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,
> > }
> >
> > static void pci_bus_distribute_available_resources(struct pci_bus *bus,
> > - struct list_head *add_list,
> > - resource_size_t available_io,
> > - resource_size_t available_mmio,
> > - resource_size_t available_mmio_pref)
> > + struct list_head *add_list, struct resource io,
> > + struct resource mmio, struct resource mmio_pref)
> > {
> > - resource_size_t remaining_io, remaining_mmio, remaining_mmio_pref;
> > + resource_size_t io_per_hp, mmio_per_hp, mmio_pref_per_hp, align;
> > unsigned int normal_bridges = 0, hotplug_bridges = 0;
> > struct resource *io_res, *mmio_res, *mmio_pref_res;
> > struct pci_dev *dev, *bridge = bus->self;
> > @@ -1850,29 +1848,36 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
> > mmio_pref_res = &bridge->resource[PCI_BRIDGE_RESOURCES + 2];
> >
> > /*
> > - * Update additional resource list (add_list) to fill all the
> > - * extra resource space available for this port except the space
> > - * calculated in __pci_bus_size_bridges() which covers all the
> > - * devices currently connected to the port and below.
> > + * The alignment of this bridge is yet to be considered, hence it must
> > + * be done now before extending its bridge window. A single bridge
> > + * might not be able to occupy the whole parent region if the alignment
> > + * differs - for example, an external GPU at the end of a Thunderbolt
> > + * daisy chain.
>
> As Bjorn also commented there is nothing Thunderbolt specific here so I
> would leave it out of the comment because it is kind of confusing.
Okay, I can remove "A single bridge.... daisy chain".
Please correct me if that is not what you meant.

>
> > */
> > - extend_bridge_window(bridge, io_res, add_list, available_io);
> > - extend_bridge_window(bridge, mmio_res, add_list, available_mmio);
> > - extend_bridge_window(bridge, mmio_pref_res, add_list,
> > - available_mmio_pref);
> > + align = pci_resource_alignment(bridge, io_res);
> > + if (!io_res->parent && align)
> > + io.start = ALIGN(io.start, align);
> > +
> > + align = pci_resource_alignment(bridge, mmio_res);
> > + if (!mmio_res->parent && align)
> > + mmio.start = ALIGN(mmio.start, align);
> > +
> > + align = pci_resource_alignment(bridge, mmio_pref_res);
> > + if (!mmio_pref_res->parent && align)
> > + mmio_pref.start = ALIGN(mmio_pref.start, align);
> >
> > /*
> > - * Calculate the total amount of extra resource space we can
> > - * pass to bridges below this one. This is basically the
> > - * extra space reduced by the minimal required space for the
> > - * non-hotplug bridges.
> > + * Update the resources to fill as much remaining resource space in the
> > + * parent bridge as possible, while considering alignment.
> > */
> > - remaining_io = available_io;
> > - remaining_mmio = available_mmio;
> > - remaining_mmio_pref = available_mmio_pref;
> > + extend_bridge_window(bridge, io_res, add_list, resource_size(&io));
> > + extend_bridge_window(bridge, mmio_res, add_list, resource_size(&mmio));
> > + extend_bridge_window(bridge, mmio_pref_res, add_list,
> > + resource_size(&mmio_pref));
>
> Please write it like it was originally (e.g align the second line to the
> opening bracket):
>
> extend_bridge_window(bridge, mmio_pref_res, add_list, resource_size(&mmio_pref));
Can do. The style of handling line overflows is still throwing me.

>
> >
> > /*
> > * Calculate how many hotplug bridges and normal bridges there
> > - * are on this bus. We will distribute the additional available
> > + * are on this bus. We will distribute the additional available
> > * resources between hotplug bridges.
> > */
> > for_each_pci_bridge(dev, bus) {
> > @@ -1882,104 +1887,98 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
> > normal_bridges++;
> > }
> >
> > + /*
> > + * There is only one bridge on the bus so it gets all possible
> > + * resources which it can then distribute to the possible
> > + * hotplug bridges below.
> > + */
> > + if (hotplug_bridges + normal_bridges == 1) {
> > + dev = list_first_entry(&bus->devices, struct pci_dev, bus_list);
> > + if (dev->subordinate)
> > + pci_bus_distribute_available_resources(dev->subordinate,
> > + add_list, io, mmio, mmio_pref);
> > + return;
> > + }
> > +
> > + /*
> > + * Reduce the available resource space by what the
> > + * bridge and devices below it occupy.
> > + */
> > for_each_pci_bridge(dev, bus) {
> > - const struct resource *res;
> > + struct resource *res;
> > + resource_size_t used_size;
>
> Here order these in "reverse christmas tree" like:
>
> resource_size_t used_size;
> struct resource *res;
That seems reasonable.

>
> >
> > if (dev->is_hotplug_bridge)
> > continue;
> >
> > - /*
> > - * Reduce the available resource space by what the
> > - * bridge and devices below it occupy.
> > - */
> > res = &dev->resource[PCI_BRIDGE_RESOURCES + 0];
> > - if (!res->parent && available_io > resource_size(res))
> > - remaining_io -= resource_size(res);
> > + align = pci_resource_alignment(dev, res);
> > + align = align ? ALIGN(io.start, align) - io.start : 0;
> > + used_size = align + resource_size(res);
> > + if (!res->parent && used_size <= resource_size(&io))
> > + io.start += used_size;
> >
> > res = &dev->resource[PCI_BRIDGE_RESOURCES + 1];
> > - if (!res->parent && available_mmio > resource_size(res))
> > - remaining_mmio -= resource_size(res);
> > + align = pci_resource_alignment(dev, res);
> > + align = align ? ALIGN(mmio.start, align) - mmio.start : 0;
> > + used_size = align + resource_size(res);
> > + if (!res->parent && used_size <= resource_size(&mmio))
> > + mmio.start += used_size;
> >
> > res = &dev->resource[PCI_BRIDGE_RESOURCES + 2];
> > - if (!res->parent && available_mmio_pref > resource_size(res))
> > - remaining_mmio_pref -= resource_size(res);
> > + align = pci_resource_alignment(dev, res);
> > + align = align ? ALIGN(mmio_pref.start, align) -
> > + mmio_pref.start : 0;
> > + used_size = align + resource_size(res);
> > + if (!res->parent && used_size <= resource_size(&mmio_pref))
> > + mmio_pref.start += used_size;
> > }
> >
> > - /*
> > - * There is only one bridge on the bus so it gets all available
> > - * resources which it can then distribute to the possible hotplug
> > - * bridges below.
> > - */
> > - if (hotplug_bridges + normal_bridges == 1) {
> > - dev = list_first_entry(&bus->devices, struct pci_dev, bus_list);
> > - if (dev->subordinate) {
> > - pci_bus_distribute_available_resources(dev->subordinate,
> > - add_list, available_io, available_mmio,
> > - available_mmio_pref);
> > - }
> > + if (!hotplug_bridges)
> > return;
> > - }
> >
> > /*
> > - * Go over devices on this bus and distribute the remaining
> > - * resource space between hotplug bridges.
> > + * Distribute any remaining resources equally between
> > + * the hotplug-capable downstream ports.
> > */
> > - for_each_pci_bridge(dev, bus) {
> > - resource_size_t align, io, mmio, mmio_pref;
> > - struct pci_bus *b;
> > + io_per_hp = div64_ul(resource_size(&io), hotplug_bridges);
> > + mmio_per_hp = div64_ul(resource_size(&mmio), hotplug_bridges);
> > + mmio_pref_per_hp = div64_ul(resource_size(&mmio_pref),
> > + hotplug_bridges);
>
> Here also write it like:
>
> mmio_pref_per_hp = div64_ul(resource_size(&mmio_pref),
> hotplug_bridges);
Okay.

>
> >
> > - b = dev->subordinate;
> > - if (!b || !dev->is_hotplug_bridge)
> > + for_each_pci_bridge(dev, bus) {
> > + if (!dev->subordinate || !dev->is_hotplug_bridge)
> > continue;
> >
> > - /*
> > - * Distribute available extra resources equally between
> > - * hotplug-capable downstream ports taking alignment into
> > - * account.
> > - *
> > - * Here hotplug_bridges is always != 0.
> > - */
> > - align = pci_resource_alignment(bridge, io_res);
> > - io = div64_ul(available_io, hotplug_bridges);
> > - io = min(ALIGN(io, align), remaining_io);
> > - remaining_io -= io;
> > -
> > - align = pci_resource_alignment(bridge, mmio_res);
> > - mmio = div64_ul(available_mmio, hotplug_bridges);
> > - mmio = min(ALIGN(mmio, align), remaining_mmio);
> > - remaining_mmio -= mmio;
> > + io.end = io.start + io_per_hp - 1;
> > + mmio.end = mmio.start + mmio_per_hp - 1;
> > + mmio_pref.end = mmio_pref.start + mmio_pref_per_hp - 1;
> >
> > - align = pci_resource_alignment(bridge, mmio_pref_res);
> > - mmio_pref = div64_ul(available_mmio_pref, hotplug_bridges);
> > - mmio_pref = min(ALIGN(mmio_pref, align), remaining_mmio_pref);
> > - remaining_mmio_pref -= mmio_pref;
> > + pci_bus_distribute_available_resources(dev->subordinate,
> > + add_list, io, mmio, mmio_pref);
>
> Ditto.
Okay.

>
> >
> > - pci_bus_distribute_available_resources(b, add_list, io, mmio,
> > - mmio_pref);
> > + io.start = io.end + 1;
> > + mmio.start = mmio.end + 1;
> > + mmio_pref.start = mmio_pref.end + 1;
> > }
> > }
> >
> > static void pci_bridge_distribute_available_resources(struct pci_dev *bridge,
> > struct list_head *add_list)
> > {
> > - resource_size_t available_io, available_mmio, available_mmio_pref;
> > - const struct resource *res;
> > + struct resource io_res, mmio_res, mmio_pref_res;
> >
> > if (!bridge->is_hotplug_bridge)
> > return;
> >
> > + io_res = bridge->resource[PCI_BRIDGE_RESOURCES + 0];
> > + mmio_res = bridge->resource[PCI_BRIDGE_RESOURCES + 1];
> > + mmio_pref_res = bridge->resource[PCI_BRIDGE_RESOURCES + 2];
> > +
> > /* Take the initial extra resources from the hotplug port */
> > - res = &bridge->resource[PCI_BRIDGE_RESOURCES + 0];
> > - available_io = resource_size(res);
> > - res = &bridge->resource[PCI_BRIDGE_RESOURCES + 1];
> > - available_mmio = resource_size(res);
> > - res = &bridge->resource[PCI_BRIDGE_RESOURCES + 2];
> > - available_mmio_pref = resource_size(res);
> >
> > pci_bus_distribute_available_resources(bridge->subordinate,
> > - add_list, available_io,
> > - available_mmio,
> > - available_mmio_pref);
> > + add_list, io_res, mmio_res, mmio_pref_res);
> > }
> >
> > void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge)
> > --
> > 2.20.1
> >