Hi,
recently I met a problem with pci bus resource allocation. The allocation strategy
makes me confused and leads to a wrong allocation results.
There is a hisilicon network device with four functions under one root port. The
original bios resources allocation looks like:
7c:00.0 Root Port
prefetchable memory behind bridge: 12000000-0x1210fffff 17M [64bit pref]
7d:00.0
bar0: 0x121000000-0x12100ffff 64k [64bit pref]
bar2: 0x120000000-0x1200fffff 1M [64bit pref]
bar7: 0x121010000-0x12103ffff 128K [64bit pref]
bar9: 0x120100000-0x1203fffff 3M [64bit pref]
7d:00.1
bar0: 0x121040000-0x12104ffff 64k [64bit pref]
bar2: 0x120400000-0x1204fffff 1M [64bit pref]
bar7: 0x121050000-0x12107ffff 128K [64bit pref]
bar9: 0x120500000-0x1207fffff 3M [64bit pref]
7d:00.2
bar0: 0x121080000-0x12108ffff 64k [64bit pref]
bar2: 0x120800000-0x1208fffff 1M [64bit pref]
bar7: 0x121090000-0x1210bffff 128K [64bit pref]
bar9: 0x120900000-0x120bfffff 3M [64bit pref]
7d:00.3
bar0: 0x1210c0000-0x1210cffff 64k [64bit pref]
bar2: 0x120c00000-0x120cfffff 1M [64bit pref]
bar7: 0x121010000-0x12103ffff 128K [64bit pref]
bar9: 0x120d00000-0x120ffffff 3M [64bit pref]
When I remove function 7d:00.3 and try to rescan the bus[7c], kernel prints the
error information.
[ 391.770030] pci 0000:7d:00.3: [19e5:a221] type 00 class 0x020000
[ 391.776024] pci 0000:7d:00.3: reg 0x10: [mem 0x1210c0000-0x1210cffff 64bit pref]
[ 391.783394] pci 0000:7d:00.3: reg 0x18: [mem 0x120c00000-0x120cfffff 64bit pref]
[ 391.790786] pci 0000:7d:00.3: reg 0x224: [mem 0x1210d0000-0x1210dffff 64bit pref]
[ 391.798238] pci 0000:7d:00.3: VF(n) BAR0 space: [mem 0x1210d0000-0x1210fffff 64bit pref] (contains BAR0 for 3 VFs)
[ 391.808543] pci 0000:7d:00.3: reg 0x22c: [mem 0x120d00000-0x120dfffff 64bit pref]
[ 391.815994] pci 0000:7d:00.3: VF(n) BAR2 space: [mem 0x120d00000-0x120ffffff 64bit pref] (contains BAR2 for 3 VFs)
[ 391.826391] pci 0000:7c:00.0: bridge window [mem 0x00100000-0x002fffff] to [bus 7d] add_size 300000 add_align 100000
[ 391.836869] pci 0000:7c:00.0: BAR 14: no space for [mem size 0x00500000]
^^^^^^^^^^^^^^^^^^^^^^^
[ 391.843543] pci 0000:7c:00.0: BAR 14: failed to assign [mem size 0x00500000]
^^^^^^^^^^^^^^^^^^^^^^^^^
[ 391.850562] pci 0000:7c:00.0: BAR 14: no space for [mem size 0x00200000]
^^^^^^^^^^^^^^^^^^^^^^^
[ 391.857237] pci 0000:7c:00.0: BAR 14: failed to assign [mem size 0x00200000]
^^^^^^^^^^^^^^^^^^^^^^^^^
[ 391.864261] pci 0000:7d:00.3: BAR 2: assigned [mem 0x120c00000-0x120cfffff 64bit pref]
[ 391.872148] pci 0000:7d:00.3: BAR 9: assigned [mem 0x120d00000-0x120ffffff 64bit pref]
[ 391.880035] pci 0000:7d:00.3: BAR 0: assigned [mem 0x1210c0000-0x1210cffff 64bit pref]
[ 391.887920] pci 0000:7d:00.3: BAR 7: assigned [mem 0x1210d0000-0x1210fffff 64bit pref]
When looking into the code, the functions called like:
pci_rescan_bus()
pci_assign_unassigned_bus_resources()
__pci_bus_size_bridges()
pbus_size_mem()
The function 7d:00.3 is added and enabled well as the required resources are satisfied.
As it request 64bit prefetchable resources, there is no reason to open bar14 for it.
When a new function is added, the framework trys to size the bridge memory
window for it. In __pci_bus_size_bridges(), firstly the framework trys to size bar15 for the
new added 5M resources as we require 64bit pref mem. But bar15 has *parent*
so pbus_size_mem() return failure with bar15 unchanged. Then the framework try to put
resources in bar14, 32bit mem window, and the bar14 is unused so it is sized to 5M and
pbus_size_mem() return success.
After bridge size settles down, the framework assign resources for each bar. *As the bios
doesn't reserve a 32bit mem window for the bridge*, bar14 assignment is failed and print
the error assigen information. When assigning 7d:00.3, the framework try to find a space
in bar15 firstly and succeed. Then the flow is terminated. The bar14 is even not touched.
Here comes the question:
Why should we resize the bridge memory window when only one function is removed and
rescanned later? The bridge memory window should remain unchanged in such a situation.
Is there a *certain condition* which requirs such operation?
If all the functions are removed, we should use pci_rescan_bus_bridge_resize() to rescan and add
devices as the required memory size maybe changed. Otherwise, i think we should try to assign
resources directly without sizing the bridge resource.
Thanks,
Yang
