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Documentation: Add section about 'hidden' devices to 4.13 release notes 

CB:41384 (SHA dbcf7b1621) added some new
functionality to devicetree files ("hidden PCI devices"). It's a decent
enough semantic change that it should be added to the release notes for
the 4.13 release.

Change-Id: I52969f63dbc492afd32279176cbcfc2b76d7ac33
Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41563
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
This commit is contained in:
Tim Wawrzynczak 2020-05-20 10:05:08 -06:00
parent 554b03038e
commit a4e2e0550c
1 changed files with 15 additions and 0 deletions
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15
Documentation/releases/coreboot-4.13-relnotes.md
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@ -13,4 +13,19 @@ Update this document with changes that should be in the release notes.
Significant changes Significant changes
------------------- -------------------
### Hidden PCI devices
This new functionality takes advantage of the existing 'hidden' keyword in the
devicetree. Since no existing boards were using the keyword, its usage was
repurposed to make dealing with some unique PCI devices easier. The particular
case here is Intel's PMC (Power Management Controller). During the FSP-S run,
the PMC device is made hidden, meaning that its config space looks as if there
is no device there (Vendor ID reads as 0xFFFF_FFFF). However, the device does
have fixed resources, both MMIO and I/O. These were previously recorded in
different places (MMIO was typically an SA fixed resource, and I/O was treated
as an LPC resource). With this change, when a device in the tree is marked as
'hidden', it is not probed (`pci_probe_dev()`) but rather assumed to exist so
that its resources can be placed in a more natural location. This also adds the
ability for the device to participate in SSDT generation.
### Add significant changes here ### Add significant changes here