[i-g-t] lib/igt_kms: Choose default mode based on --environment flag from igt_runner

[Bhanuprakash Modem]

igt_runner provides --environment flag KEY=VALUE pair as the environment
variable to execute test processes. Upon user request igt_runner will set
an environment variable to choose default DRM display mode for subtests
instead of taking the preferred mode.

Example:
Eventhough we have an 8K panel, Kernel may expose 4K or lesser mode
as a preferred mode. So all subtests will take this mode as a default
may cause losing the coverage.

This patch will parse the environment variable exposed by igt_runner
and take the decision to choose the mode from the available list.

Possible options are:
  0: Choose the mode with lowest possible resolution.
  1: Choose the mode with highest possible resolution.

By default (without this flag) fallback to take the preferred mode exposed
by the Kernel.

Usage:
./igt_runner --environment "IGT_KMS_RESOLUTION=1" ...

Cc: Petri Latvala <petri.latvala at intel.com>
Cc: Swati Sharma <swati2.sharma at intel.com>
Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem at intel.com>
---
 lib/igt_kms.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/igt_kms.c b/lib/igt_kms.c
index 14064614..02c43dd6 100644
--- a/lib/igt_kms.c
+++ b/lib/igt_kms.c
@@ -1586,7 +1586,8 @@ void igt_sort_connector_modes(drmModeConnector *connector,
 bool kmstest_get_connector_default_mode(int drm_fd, drmModeConnector *connector,
 					drmModeModeInfo *mode)
 {
-	int i;
+	char *env;
+	int i, res;
 
 	if (!connector->count_modes) {
 		igt_warn("no modes for connector %d\n",
@@ -1594,6 +1595,26 @@ bool kmstest_get_connector_default_mode(int drm_fd, drmModeConnector *connector,
 		return false;
 	}
 
+	env = getenv("IGT_KMS_RESOLUTION");
+	if (env) {
+		res = atoi(env);
+
+		/*
+		 * Only 0 and 1 are allowed.
+		 * 0: Choose connector mode with lowest possible resolution.
+		 * 1: Choose connector mode with highest possible resolution.
+		 */
+		if (res != 0 && res != 1)
+			goto default_mode;
+
+		igt_sort_connector_modes(connector, res ?
+						     sort_drm_modes_by_res_dsc :
+						     sort_drm_modes_by_res_asc);
+		*mode = connector->modes[0];
+		return true;
+	}
+
+default_mode:
 	for (i = 0; i < connector->count_modes; i++) {
 		if (i == 0 ||
 		    connector->modes[i].type & DRM_MODE_TYPE_PREFERRED) {
-- 
2.35.1