[UBUNTU 20.04] ZPCI used write back addresses by default but should use write through

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In the initial MIO support introduced in

commit 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions")

setting up the PCI BAR resources defaults to using the
mio_wb address as the resource's start address.

This means users of the mapping, which includes most drivers, will get write combining on PCI Stores.

his may lead to problems when drivers expect write through
behavior when not using an explicit ioremap_wc() which is the default
behavior on other platforms.

The attached patch changes the default to write through.
It has already been reviewed and is currently queued to be send for
Linux 5.6-rc5 with a CC stable tag.

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Default Comment by Bridge

[Frank Heimes (fheimes)]

Patch request submitted:
https://lists.ubuntu.com/archives/kernel-team/2020-March/thread.html#108082
changing status to 'In Progress'.

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------- Comment From <email address hidden> 2020-03-09 04:15 EDT-------
This has now been merged in Linus' upstream tree as

df057c914a9c219ac8b8ed22caf7da2f80c1fe26 s390/pci: Fix unexpected write combine on resource

[Frank Heimes (fheimes)]

Hi Niklas, yes, thx.
Also found the patch in 'linux-next' and cherry-picked that one.

[Frank Heimes (fheimes)]

Fix released via stable linux 5.4.25 update

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------- Comment From <email address hidden> 2020-03-17 04:16 EDT-------
IBM Bugzilla status -> closed, Fix Released with focal