PCI: endpoint: Usage of atomic notifier chain

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

Hi,

While working with the PCI endpoint subsystem, I stumbled upon the sleeping
in atomic context bug during CORE_INIT phase. The issue seems to be due to the
usage of "epc lock" (mutex) in functions such as set_msi, set_msix,
write_header, etc...

These functions are supposed to be used in the atomic notifier chain by the
CORE_INIT notifier. While using the lock is necessary in these functions as
pci_epc_create() would've been called, I see two possible workarounds:

1. Using non-atomic notifier chains such as blocking or raw.
2. Modifying the EPF drivers to use workqueue in CORE_INIT notifier chain. But
this has the implication of missing the workqueue execution before hitting other
PCI events as there might be a delay in scheduling the work item.

I prefer 1st option but I'd like to hear other ideas also.

Thanks,
Mani