From fb824da09c41b9e2cd30885a1c33e5574c3e2ca2 Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Fri, 5 Nov 2021 14:33:40 -0400
Subject: drm/dp: Don't read back backlight mode in drm_edp_backlight_enable()
Git-commit: 646596485e1ed2182adf293dfd5aec4a96c46330
Patch-mainline: v5.17-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
As it turns out, apparently some machines will actually leave additional
backlight functionality like dynamic backlight control on before the OS
loads. Currently we don't take care to disable unsupported features when
writing back the backlight mode, which can lead to some rather strange
looking behavior when adjusting the backlight.
So, let's fix this by just not reading back the current backlight mode on
initial enable. I don't think there should really be any downsides to this,
and this will ensure we don't leave any unsupported functionality enabled.
This should fix at least one (but not all) of the issues seen with DPCD
backlight support on fi-bdw-samus
v5:
* Just avoid reading back DPCD register - Doug Anderson
Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: 867cf9cd73c3 ("drm/dp: Extract i915's eDP backlight code into DRM helpers")
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211105183342.130810-4-lyude@redhat.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/drm_dp_helper.c | 40 ++++++++++-----------------------
1 file changed, 12 insertions(+), 28 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index ada0a1ff262d..af2aad2f4725 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -3363,27 +3363,13 @@ int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backli
const u16 level)
{
int ret;
- u8 dpcd_buf, new_dpcd_buf;
+ u8 dpcd_buf = DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
- ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf);
- if (ret != 1) {
- drm_dbg_kms(aux->drm_dev,
- "%s: Failed to read backlight mode: %d\n", aux->name, ret);
- return ret < 0 ? ret : -EIO;
- }
-
- new_dpcd_buf = dpcd_buf;
-
- if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
- new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
- new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
-
- if (bl->pwmgen_bit_count) {
- ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
- if (ret != 1)
- drm_dbg_kms(aux->drm_dev, "%s: Failed to write aux pwmgen bit count: %d\n",
- aux->name, ret);
- }
+ if (bl->pwmgen_bit_count) {
+ ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
+ if (ret != 1)
+ drm_dbg_kms(aux->drm_dev, "%s: Failed to write aux pwmgen bit count: %d\n",
+ aux->name, ret);
}
if (bl->pwm_freq_pre_divider) {
@@ -3393,16 +3379,14 @@ int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backli
"%s: Failed to write aux backlight frequency: %d\n",
aux->name, ret);
else
- new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
+ dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
}
- if (new_dpcd_buf != dpcd_buf) {
- ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
- if (ret != 1) {
- drm_dbg_kms(aux->drm_dev, "%s: Failed to write aux backlight mode: %d\n",
- aux->name, ret);
- return ret < 0 ? ret : -EIO;
- }
+ ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf);
+ if (ret != 1) {
+ drm_dbg_kms(aux->drm_dev, "%s: Failed to write aux backlight mode: %d\n",
+ aux->name, ret);
+ return ret < 0 ? ret : -EIO;
}
ret = drm_edp_backlight_set_level(aux, bl, level);
--
2.38.1