drm/amd/display: Read before writing Backlight Mode Set Register

Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

kernel os linux

[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 <sreeja.golui@amd.com>
Reviewed-by: Harry Vanzylldejong <harry.vanzylldejong@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Iswara Nagulendran <iswara.nagulendran@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

authored by

Iswara Nagulendran and committed by

Alex Deucher 2 years ago b231933d 1b9ec7cb

+6 -1

1 changed file

expand all

drivers

gpu

drm

amd

display

link

protocols

link_edp_panel_control.c

+6 -1

drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c

··· 182 182 &backlight_control, 1) != DC_OK) 183 183 return false; 184 184 } else { 185 - const uint8_t backlight_enable = DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE; 185 + uint8_t backlight_enable = 0; 186 186 struct target_luminance_value *target_luminance = NULL; 187 187 188 188 //if target luminance value is greater than 24 bits, clip the value to 24 bits ··· 190 190 backlight_millinits = 0xFFFFFF; 191 191 192 192 target_luminance = (struct target_luminance_value *)&backlight_millinits; 193 + 194 + core_link_read_dpcd(link, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, 195 + &backlight_enable, sizeof(uint8_t)); 196 + 197 + backlight_enable |= DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE; 193 198 194 199 if (core_link_write_dpcd(link, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, 195 200 &backlight_enable,

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