[v2,0/3] Add a test to catch unprobed Devicetree devices

Message

Nícolas F. R. A. Prado Aug. 17, 2023, 11:35 p.m. UTC

Regressions that cause a device to no longer be probed by a driver can
have a big impact on the platform's functionality, and despite being
relatively common there isn't currently any generic test to detect them.
As an example, bootrr [1] does test for device probe, but it requires
defining the expected probed devices for each platform.

Given that the Devicetree already provides a static description of
devices on the system, it is a good basis for building such a test on
top.

This series introduces a test to catch regressions that prevent devices
from probing.

Patches 1 and 2 extend the existing dt-extract-compatibles to be able to
output only the compatibles that can be expected to match a Devicetree
node to a driver. Patch 2 adds a kselftest that walks over the
Devicetree nodes on the current platform and compares the compatibles to
the ones on the list, and on an ignore list, to point out devices that
failed to be probed.

A compatible list is needed because not all compatibles that can show up
in a Devicetree node can be used to match to a driver, for example the
code for that compatible might use "OF_DECLARE" type macros and avoid
the driver framework, or the node might be controlled by a driver that
was bound to a different node.

An ignore list is needed for the few cases where it's common for a
driver to match a device but not probe, like for the "simple-mfd"
compatible, where the driver only probes if that compatible is the
node's first compatible.

The reason for parsing the kernel source instead of relying on
information exposed by the kernel at runtime (say, looking at modaliases
or introducing some other mechanism), is to be able to catch issues
where a config was renamed or a driver moved across configs, and the
.config used by the kernel not updated accordingly. We need to parse the
source to find all compatibles present in the kernel independent of the
current config being run.

[1] https://github.com/kernelci/bootrr

Changes in v2:
- Extended dt-extract-compatibles script to be able to extract driver
  matching compatibles, instead of adding a new one in Coccinelle
- Made kselftest output in the KTAP format

Nícolas F. R. A. Prado (3):
  dt: dt-extract-compatibles: Handle cfile arguments in generator
    function
  dt: dt-extract-compatibles: Add flag for driver matching compatibles
  kselftest: Add new test for detecting unprobed Devicetree devices

 scripts/dtc/dt-extract-compatibles            | 74 +++++++++++++----
 tools/testing/selftests/Makefile              |  1 +
 tools/testing/selftests/dt/.gitignore         |  1 +
 tools/testing/selftests/dt/Makefile           | 21 +++++
 .../selftests/dt/compatible_ignore_list       |  1 +
 tools/testing/selftests/dt/ktap_helpers.sh    | 57 +++++++++++++
 .../selftests/dt/test_unprobed_devices.sh     | 79 +++++++++++++++++++
 7 files changed, 218 insertions(+), 16 deletions(-)
 create mode 100644 tools/testing/selftests/dt/.gitignore
 create mode 100644 tools/testing/selftests/dt/Makefile
 create mode 100644 tools/testing/selftests/dt/compatible_ignore_list
 create mode 100644 tools/testing/selftests/dt/ktap_helpers.sh
 create mode 100755 tools/testing/selftests/dt/test_unprobed_devices.sh