Hello, Kenji-san
Kenji Kaneshige wrote:
I misunderstood the problem.
My understanding was memory resource was not enabled even though Linux
set
the Memory Space bit in the command register. But it was not correct. The
bridge memory window was marked unused and Linux didn't try to set Memory
Space bit in the command register. Current my understanding is as
follows.
Please correct me if I'm still misunderstanding something.
1) Your BIOS doesn't assign any resource to the bridge if its child PCI
hot-plug slot is not occupied.
2) At the boot time, pci_assign_unassigned_resources() try to assign
memory resouces to the bridge using pci_bus_assign_resource(), but
it was disabled because there are no devices require memory resource.
3) And then pci_assign_unassigned_resouces() calls pci_enable_bridge(),
but Memory Space bit in the command register was not set because no
memory resource are assigned to the bridge. At the same time,
pci_dev->enable_cnt was incremented.
4) At the rescan time, pci_setup_bridge() and pci_enable_bridge() doesn't
work because the bridge is already marked "enabled" (i.e.
pci_dev->enable_cnt is not zero).
I don't have any concrete idea how to fix that so far, but I can say
my idea
(pcibios_enable_device() should return an error) was wrong.
BTW, on my PCI hotplug capable system (SHPC and PCIe), I/O and Memory
windows
of the bridge are assigned by BIOS regardless of whether hotplug slot(s)
behind the bridge is occupied or not. Maybe that is the reason why I have
never encountered this problem before.
Thanks,
Kenji Kaneshige
Yes, your understanding of the problem is correct. On this platform BIOS
(bootloader, u-boot)
is not required to configure PCI, linux is capable of doing all
configuration itself. But both u-boot
and linux do not assign memory resources to bridge if there's no device
behind it.
Thanks a lot.
Felix.
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