PCI: Rework optional resource handling

Remove and rescan cycle can result in failure to assign a bridge window if
it becomes larger than before the remove. The bridge window size will
include space for disabled Expansion ROM, which can causes the bridge
window to not fit anymore into the same address space slot on rescan if the
Expansion ROM resource was not assigned before the remove. In addition, the
optional resource handling is not internally consistent.

The resource fitting logic supports three main types of optional resources:

  - IOV BARs
  - Expansion ROMs
  - Bridge window size variation due to optional resources

In addition to the above, resizable BARs beyond their current size will
require handling optional variation in resource sizes within the resource
fitting algorithm (not yet done by the resource fitting code).

There are multiple inconsistencies related to optional resource handling:

a) The allocation failure of disabled expansion ROM requires special case
   inside assign_requested_resources_sorted().

b) The optionality of disabled expansion ROM is not considered during
   bridge window sizing in pbus_size_mem().

c) Setting resource size to zero for optional resource in pbus_size_mem()
   is problematic because it makes also the alignment invalid, which is
   checked by pdev_sort_resources().

   Optional IOV resources have their size set to zero by pbus_size_mem()
   but the information about size is stored externally in struct pci_sriov
   and complex call-chain trickery in pci_resource_alignment() ensures IOV
   resources return a valid alignment despite having zero resource size. A
   solution that is specific to IOV resources makes it hard to use the same
   solution for other types of resources such as expansion ROM.

Simply changing pbus_size_mem() is not sufficient to fully address the main
issue because it would introduce disparity between bridge window sizing and
resource allocation. Due to size-based ordering of the resource list during
assignment loop, an Expansion ROM resource could steal space from some
other resource and make the other resource not fit if the Expansion ROM is
larger than the other resource. Thus, the resource assignment functions
need to be changed as well.

Make optional resource handling more straightforward. Use
pci_resource_is_optional() to determine if a resource is optional in both
bridge window sizing and assignment failure classification to ensure they
always align. Indicate with a parameter to
assign_requested_resources_sorted() whether it should attempt to allocate
optional resources or not.

Always try first to assign all resources (also when realloc_head is not
provided). This is required for calls from
pci_assign_unassigned_root_bus_resources() that provide realloc_head only
with some of its iterations.

Non-bridge-window optional resources in realloc_head now have add_size 0.
This condition has to be detected in reassign_resources_sorted() before
reassigning them (which would fail as there is no size change).  Removing
add_size=0 optional resources entirely from realloc_head might eventually
be doable but further rework in __assign_resources_sorted() is needed first
to support such a change.

Link: https://lore.kernel.org/r/20241216175632.4175-26-ilpo.jarvinen@linux.intel.com
Reported-by: Jia Yao <jia.yao@intel.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219547
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Jia Yao <jia.yao@intel.com>
Tested-by: Xiaochun Lee <lixc17@lenovo.com>

0 files changed, 0 insertions, 0 deletions