From b231933da7d6be53d08139f8adf2560a90b47ca9 Mon Sep 17 00:00:00 2001 From: Iswara Nagulendran Date: Fri, 29 Sep 2023 11:20:46 -0400 Subject: [PATCH] drm/amd/display: Read before writing Backlight Mode Set Register [HOW&WHY] Reading the value from DP_EDP_BACKLIGHT_MODE_SET_REGISTER, DPCD 0x721 before setting the BP_EDP_PANEL_LUMINANC_CONTROL_ENABLE bit to ensure there are no accidental overwrites. Reviewed-by: Sreeja Golui Reviewed-by: Harry Vanzylldejong Acked-by: Roman Li Signed-off-by: Iswara Nagulendran Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher --- .../amd/display/dc/link/protocols/link_edp_panel_control.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c index 86f97ddcc595..e32a7974a4bc 100644 --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c @@ -182,7 +182,7 @@ bool edp_set_backlight_level_nits(struct dc_link *link, &backlight_control, 1) != DC_OK) return false; } else { - const uint8_t backlight_enable = DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE; + uint8_t backlight_enable = 0; struct target_luminance_value *target_luminance = NULL; //if target luminance value is greater than 24 bits, clip the value to 24 bits @@ -191,6 +191,11 @@ bool edp_set_backlight_level_nits(struct dc_link *link, target_luminance = (struct target_luminance_value *)&backlight_millinits; + core_link_read_dpcd(link, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, + &backlight_enable, sizeof(uint8_t)); + + backlight_enable |= DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE; + if (core_link_write_dpcd(link, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &backlight_enable, sizeof(backlight_enable)) != DC_OK) -- 2.39.5