[PATCH] drm/i915/quirk: Add quirk for devices that cannot be dimmed

[Allen Ballway]

Cybernet T10C cannot be dimmed without the backlight strobing. Create a
new quirk to lock the minimum brightness to the highest supported value.
This aligns the device with its behavior on Windows, which will not
lower the brightness below maximum.

Signed-off-by: Allen Ballway <ballway at chromium.org>
---
V2 -> V3: Fix typo.
V1 -> V2: Fix style issue.

.../gpu/drm/i915/display/intel_backlight.c    |  5 ++++
 drivers/gpu/drm/i915/display/intel_quirks.c   | 27 +++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_quirks.h   |  1 +
 3 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
index 2e8f17c045222..f015563d3ebd5 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -1192,6 +1192,11 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector)

 	drm_WARN_ON(&i915->drm, panel->backlight.pwm_level_max == 0);

+	if (intel_has_quirk(i915, QUIRK_NO_DIM)) {
+		/* Cannot dim backlight, set minimum to highest value */
+		return panel->backlight.pwm_level_max - 1;
+	}
+
 	/*
 	 * XXX: If the vbt value is 255, it makes min equal to max, which leads
 	 * to problems. There are such machines out there. Either our
diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c b/drivers/gpu/drm/i915/display/intel_quirks.c
index a280448df771a..910c95840a539 100644
--- a/drivers/gpu/drm/i915/display/intel_quirks.c
+++ b/drivers/gpu/drm/i915/display/intel_quirks.c
@@ -65,6 +65,12 @@ static void quirk_no_pps_backlight_power_hook(struct drm_i915_private *i915)
 	drm_info(&i915->drm, "Applying no pps backlight power quirk\n");
 }

+static void quirk_no_dim(struct drm_i915_private *i915)
+{
+	intel_set_quirk(i915, QUIRK_NO_DIM);
+	drm_info(&i915->drm, "Applying no dim quirk\n");
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;
@@ -90,6 +96,12 @@ static int intel_dmi_no_pps_backlight(const struct dmi_system_id *id)
 	return 1;
 }

+static int intel_dmi_no_dim(const struct dmi_system_id *id)
+{
+	DRM_INFO("No dimming allowed on %s\n", id->ident);
+	return 1;
+}
+
 static const struct intel_dmi_quirk intel_dmi_quirks[] = {
 	{
 		.dmi_id_list = &(const struct dmi_system_id[]) {
@@ -136,6 +148,20 @@ static const struct intel_dmi_quirk intel_dmi_quirks[] = {
 		},
 		.hook = quirk_no_pps_backlight_power_hook,
 	},
+	{
+		.dmi_id_list = &(const struct dmi_system_id[]) {
+			{
+				.callback = intel_dmi_no_dim,
+				.ident = "Cybernet T10C Tablet",
+				.matches = {DMI_EXACT_MATCH(DMI_BOARD_VENDOR,
+							    "Cybernet Manufacturing Inc."),
+					    DMI_EXACT_MATCH(DMI_BOARD_NAME, "T10C Tablet"),
+				},
+			},
+			{ }
+		},
+		.hook = quirk_no_dim,
+	},
 };

 static struct intel_quirk intel_quirks[] = {
@@ -218,6 +244,7 @@ void intel_init_quirks(struct drm_i915_private *i915)
 		     q->subsystem_device == PCI_ANY_ID))
 			q->hook(i915);
 	}
+
 	for (i = 0; i < ARRAY_SIZE(intel_dmi_quirks); i++) {
 		if (dmi_check_system(*intel_dmi_quirks[i].dmi_id_list) != 0)
 			intel_dmi_quirks[i].hook(i915);
diff --git a/drivers/gpu/drm/i915/display/intel_quirks.h b/drivers/gpu/drm/i915/display/intel_quirks.h
index 10a4d163149fd..b41c7bbf0a5e3 100644
--- a/drivers/gpu/drm/i915/display/intel_quirks.h
+++ b/drivers/gpu/drm/i915/display/intel_quirks.h
@@ -17,6 +17,7 @@ enum intel_quirk_id {
 	QUIRK_INVERT_BRIGHTNESS,
 	QUIRK_LVDS_SSC_DISABLE,
 	QUIRK_NO_PPS_BACKLIGHT_POWER_HOOK,
+	QUIRK_NO_DIM,
 };

 void intel_init_quirks(struct drm_i915_private *i915);
--
2.41.0.255.g8b1d071c50-goog