[PATCH 3/5] drm/dp: Add drm_dp_psr_need_train_on_exit()

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Add a small helper to parse from the DPCD whether link training
is required when exiting PSR main-link off mode.

Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 14 ++++++++++++++
 include/drm/drm_dp_helper.h     |  1 +
 2 files changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 71309778f3d3..9c0a3e966d0d 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -850,3 +850,17 @@ int drm_dp_psr_setup_time(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE])
 	return psr_setup_time_us[i];
 }
 EXPORT_SYMBOL(drm_dp_psr_setup_time);
+
+/**
+ * drm_dp_psr_need_train_on_exit() - Indicate whether link training is needed on PSR exit
+ * @psr_cap: PSR capabilities from DPCD
+ *
+ * Returns:
+ * Whether link training is required when exiting PSR main-link off mode.
+ */
+bool drm_dp_psr_need_train_on_exit(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE])
+{
+	/* DP_PSR_NO_TRAIN_ON_EXIT is "don't care" for PSR2 capable devices */
+	return psr_cap[0] < 0x2 && (psr_cap[1] & DP_PSR_NO_TRAIN_ON_EXIT) == 0;
+}
+EXPORT_SYMBOL(drm_dp_psr_need_train_on_exit);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 6aa74f7d45b4..2437f1b6e776 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -658,6 +658,7 @@ struct edp_vsc_psr {
 #define EDP_VSC_PSR_CRC_VALUES_VALID	(1<<2)
 
 int drm_dp_psr_setup_time(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE]);
+bool drm_dp_psr_need_train_on_exit(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE]);
 
 static inline int
 drm_dp_max_link_rate(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
-- 
2.7.4