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From: Douglas Anderson <dianders@chromium.org>
To: dri-devel@lists.freedesktop.org
Cc: devicetree@vger.kernel.org, steev@kali.org,
	robert.foss@linaro.org, Laurent.pinchart@ideasonboard.com,
	bjorn.andersson@linaro.org, daniel@ffwll.ch, airlied@linux.ie,
	jernej.skrabec@gmail.com, maarten.lankhorst@linux.intel.com,
	rodrigo.vivi@intel.com, sam@ravnborg.org, jonas@kwiboo.se,
	mripard@kernel.org, thierry.reding@gmail.com, lyude@redhat.com,
	linus.walleij@linaro.org, rajeevny@codeaurora.org,
	linux-arm-msm@vger.kernel.org, a.hajda@samsung.com,
	tzimmermann@suse.de, narmstrong@baylibre.com,
	Douglas Anderson <dianders@chromium.org>,
	Sean Paul <seanpaul@chromium.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/6] drm/dp: Don't zero PWMGEN_BIT_COUNT when driver_pwm_freq_hz not specified
Date: Fri, 30 Jul 2021 08:46:00 -0700	[thread overview]
Message-ID: <20210730084534.v2.1.If017efce7116ae8ba015ed7def840c390a0e0c77@changeid> (raw)
In-Reply-To: <20210730154605.2843418-1-dianders@chromium.org>

The function drm_edp_backlight_init() is defined such that the
"driver_pwm_freq_hz" parameter is optional--it's 0 if you don't want
to futz with it. If you follow this variable through, you'll find out
that if it's 0 we won't ever set the "bl->pwmgen_bit_count", leaving
it as 0.

That means that before using it in drm_edp_backlight_enable() we need
to check to see if it's non-zero.

Programming this field to zero was confusing the panel I tested with
(Samsung ATNA33XC20). The backlight still worked somewhat but the
brightness values didn't correspond to what they should have been.

Fixes: 867cf9cd73c3 ("drm/dp: Extract i915's eDP backlight code into DRM helpers")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/drm_dp_helper.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index b5f75ca05774..b8a5c5e49d74 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -3229,10 +3229,12 @@ int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backli
 		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
 		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
 
-		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) {
-- 
2.32.0.554.ge1b32706d8-goog


  reply	other threads:[~2021-07-30 15:46 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 15:45 [PATCH v2 0/6] drm/panel: atna33xc20: Fix the Samsung ATNA33XC20 panel Douglas Anderson
2021-07-30 15:46 ` Douglas Anderson [this message]
2021-07-30 15:46 ` [PATCH v2 2/6] drm/bridge: ti-sn65dsi86: Fix power off sequence Douglas Anderson
2021-07-30 15:46 ` [PATCH v2 3/6] drm/bridge: ti-sn65dsi86: Add some 100 us delays Douglas Anderson
2021-07-30 15:46 ` [PATCH v2 4/6] Revert "drm/panel-simple: Add Samsung ATNA33XC20" Douglas Anderson
2021-07-30 15:46 ` [PATCH v2 5/6] Revert "drm/panel-simple: Support for delays between GPIO & regulator" Douglas Anderson
2021-07-30 15:46 ` [PATCH v2 6/6] drm/panel: atna33xc20: Introduce the Samsung ATNA33XC20 panel Douglas Anderson

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