Add edid-decode testing infrastructure

Add two small shell utilities to generate and compare diffs between
edid-decode and di-edid-decode. Store the diffs in-tree and add tests
to ensure they don't regress. Run the tests in CI with a pinned
installation of edid-decode.

One EDID blob is added to the test collection: dell-2408wfp-dp. It's
extracted [1] from the edid-decode repository.

[1]: https://git.linuxtv.org/edid-decode.git/tree/data/dell-2408wfp-dp

Signed-off-by: Simon Ser <contact@emersion.fr>
Closes: https://gitlab.freedesktop.org/emersion/libdisplay-info/-/issues/5

.gitlab-ci.yml

@@ -1,4 +1,4 @@
-.templates_sha: &templates_sha 3e66ea37e5672bb8f48e3056ba92915b5fc5b888
+.templates_sha: &templates_sha 3f37cc0e461f5b0c815409bf6f55759f26a74e9c
 
 include:
   - project: 'freedesktop/ci-templates'
@@ -8,9 +8,13 @@ include:
     ref: *templates_sha
     file: '/templates/alpine.yml'
 
+# When updating the prepare-container step, make sure to bump
+# FDO_DISTRIBUTION_TAG, otherwise the container won't get rebuilt.
+# FDO_FORCE_REBUILD can be used when testing container changes.
 variables:
   FDO_UPSTREAM_REPO: 'emersion/libdisplay-info'
-  FDO_DISTRIBUTION_TAG: '2022-03-24.2'
+  FDO_DISTRIBUTION_TAG: '2022-03-28.0'
+  #FDO_FORCE_REBUILD: 1
 
 stages:
   - "Contribution checks"
@@ -32,7 +36,15 @@ prepare-container:
   extends: .fdo.container-build@alpine@x86_64
   stage: "Prepare container"
   variables:
-    FDO_DISTRIBUTION_PACKAGES: 'build-base meson'
+    FDO_DISTRIBUTION_PACKAGES: 'build-base meson make git'
+    FDO_DISTRIBUTION_EXEC: |
+      git clone git://linuxtv.org/edid-decode.git
+      cd edid-decode
+      git checkout 8a8d673d738ce010ca32a179032e8f6c0bb5dfb4
+      make
+      make install
+      cd ..
+      rm -rf edid-decode
   rules:
     - when: on_success
 

README.md

@@ -18,7 +18,16 @@ particular, each commit must carry a Signed-off-by tag to denote that the
 submitter adheres to the [Developer Certificate of Origin 1.1]. This project
 follows the [freedesktop.org Contributor Covenant].
 
+## Testing
+
+The low-level EDID library is tested against [edid-decode]. `test/data/`
+contains a small collection of EDID blobs and diffs between upstream
+`edid-decode` and our `di-edid-decode` clone. Our CI ensures the diffs are
+up-to-date. A patch should never make the diffs grow larger. To add a new EDID
+blob or update a diff, use `test/edid-decode-diff.sh test/data/<edid>`.
+
 [GitLab project]: https://gitlab.freedesktop.org/emersion/libdisplay-info
 [Wayland contribution guidelines]: https://gitlab.freedesktop.org/wayland/wayland/-/blob/main/CONTRIBUTING.md
 [Developer Certificate of Origin 1.1]: https://developercertificate.org/
 [freedesktop.org Contributor Covenant]: https://www.freedesktop.org/wiki/CodeOfConduct/
+[edid-decode]: https://git.linuxtv.org/edid-decode.git/

meson.build

@@ -3,7 +3,7 @@ project(
 	'c',
 	version: '0.0.0',
 	license: 'MIT',
-	meson_version: '>= 0.52.1',
+	meson_version: '>= 0.55.0',
 	default_options: [
 		'c_std=c11',
 		'warning_level=3',
@@ -51,9 +51,11 @@ di_dep = declare_dependency(
 	include_directories: include_directories('include'),
 )
 
-executable(
+di_edid_decode = executable(
 	'di-edid-decode',
 	'di-edid-decode.c',
 	dependencies: di_dep,
 	install: true,
 )
+
+subdir('test')

test/data/dell-2408wfp-dp.diff

@@ -0,0 +1,42 @@
+--- ref
++++ di
+@@ -5,39 +5,3 @@
+     Model: 41003
+     Serial Number: 842091859
+     Made in: week 47 of 2008
+-  Basic Display Parameters & Features:
+-    Digital display
+-    Bits per primary color channel: 8
+-    DisplayPort interface
+-    Maximum image size: 52 cm x 32 cm
+-    Gamma: 2.20
+-    DPMS levels: Off
+-    Supported color formats: RGB 4:4:4
+-    First detailed timing includes the native pixel format and preferred refresh rate
+-  Color Characteristics:
+-    Red  : 0.6738, 0.3193
+-    Green: 0.1875, 0.7060
+-    Blue : 0.1484, 0.0644
+-    White: 0.3134, 0.3291
+-  Established Timings I & II:
+-    IBM     :   720x400    70.081663 Hz   9:5     31.467 kHz     28.320000 MHz
+-    DMT 0x04:   640x480    59.940476 Hz   4:3     31.469 kHz     25.175000 MHz
+-    DMT 0x06:   640x480    75.000000 Hz   4:3     37.500 kHz     31.500000 MHz
+-    DMT 0x09:   800x600    60.316541 Hz   4:3     37.879 kHz     40.000000 MHz
+-    DMT 0x0b:   800x600    75.000000 Hz   4:3     46.875 kHz     49.500000 MHz
+-    DMT 0x10:  1024x768    60.003840 Hz   4:3     48.363 kHz     65.000000 MHz
+-    DMT 0x12:  1024x768    75.028582 Hz   4:3     60.023 kHz     78.750000 MHz
+-    DMT 0x24:  1280x1024   75.024675 Hz   5:4     79.976 kHz    135.000000 MHz
+-  Standard Timings:
+-    DMT 0x23:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz
+-    DMT 0x33:  1600x1200   60.000000 Hz   4:3     75.000 kHz    162.000000 MHz
+-    DMT 0x15:  1152x864    75.000000 Hz   4:3     67.500 kHz    108.000000 MHz
+-  Detailed Timing Descriptors:
+-    DTD 1:  1920x1200   59.950171 Hz   8:5     74.038 kHz    154.000000 MHz (519 mm x 320 mm)
+-                 Hfront   48 Hsync  32 Hback   80 Hpol P
+-                 Vfront    3 Vsync   6 Vback   26 Vpol N
+-    Display Product Serial Number: 'G283H8BI21MS'
+-    Display Product Name: 'DELL 2408WFP'
+-    Display Range Limits:
+-      Monitor ranges (Bare Limits): 56-76 Hz V, 30-83 kHz H, max dotclock 170 MHz
+-Checksum: 0x92

test/edid-decode-check.sh

@@ -0,0 +1,17 @@
+#!/bin/sh -eu
+
+workdir="$(mktemp -d)"
+cleanup() {
+	rm -rf "$workdir"
+}
+trap cleanup EXIT
+
+edid="$1"
+"$REF_EDID_DECODE" -s <"$edid" >"$workdir/ref"
+"$DI_EDID_DECODE" <"$edid" >"$workdir/di"
+
+if [ -f "$edid.diff" ]; then
+	patch "$workdir/ref" "$edid.diff"
+fi
+
+diff -u "$workdir/ref" "$workdir/di"

test/edid-decode-diff.sh

@@ -0,0 +1,20 @@
+#!/bin/sh -eu
+
+REF_EDID_DECODE="${REF_EDID_DECODE:-edid-decode}"
+DI_EDID_DECODE="${DI_EDID_DECODE:-di-edid-decode}"
+
+workdir="$(mktemp -d)"
+cleanup() {
+	rm -rf "$workdir"
+}
+trap cleanup EXIT
+
+for edid in "$@"; do
+	"$REF_EDID_DECODE" -s <"$edid" >"$workdir/ref"
+	"$DI_EDID_DECODE" <"$edid" >"$workdir/di"
+	if ! diff -u --label ref "$workdir/ref" --label di "$workdir/di" >"$workdir/diff"; then
+		cp "$workdir/diff" "$edid.diff"
+	else
+		rm "$edid.diff"
+	fi
+done

test/meson.build

@@ -0,0 +1,24 @@
+ref_edid_decode = find_program('edid-decode', native: true, required: false)
+if not ref_edid_decode.found()
+	test('edid-decode-not-found', find_program('false'))
+	subdir_done()
+endif
+
+test_harness = find_program('./edid-decode-check.sh', native: true)
+
+test_cases = [
+	'dell-2408wfp-dp',
+]
+
+foreach tc : test_cases
+	test(
+		tc,
+		test_harness,
+		args: [files('data/' + tc)],
+		env: [
+			'REF_EDID_DECODE=' + ref_edid_decode.full_path(),
+			'DI_EDID_DECODE=' + di_edid_decode.full_path(),
+		],
+		depends: [di_edid_decode],
+	)
+endforeach