drm: apple: answer eDP for the J313 backlight and cap it at 394 nits

drivers/gpu/drm/apple/dcp.c

@@ -3684,6 +3684,21 @@ static int dcp_ext_wait_pmp(struct apple_dcp *dcp)
 	return 0;
 }
 
+/*
+ * J313 BrightnessLCD::nitsToDBV rejects 395 nits and above.  iDAC 1956 is
+ * accepted and 1957 is not, so 394 is the brightest level that applies.
+ * apple,max-brightness on this panel is 420; 100% must land on 394.
+ */
+#define DCP_J313_MAX_NITS 394U
+
+static bool dcp_panel_is_j313(const struct dcp_panel_id *id,
+			      const char *compatible)
+{
+	if (compatible && !strcmp(compatible, "apple,panel-j313"))
+		return true;
+	return id && !strcmp(id->name, "J313");
+}
+
 static int dcp_comp_bind_pipe(struct device *dev, struct device *main, void *data)
 {
 	struct device_node *panel_np;
@@ -3769,7 +3784,7 @@ static int dcp_comp_bind_pipe(struct device *dev, struct device *main, void *dat
 
 	if (panel_np) {
 		const char height_prop[2][16] = { "adj-height-mm", "height-mm" };
-		const char *compatible;
+		const char *compatible = NULL;
 
 		if (of_device_is_available(panel_np)) {
 			ret = of_property_read_u32(panel_np, "apple,max-brightness",
@@ -3782,11 +3797,25 @@ static int dcp_comp_bind_pipe(struct device *dev, struct device *main, void *dat
 		/* use adjusted height as long as the notch is hidden */
 		of_property_read_u32(panel_np, height_prop[!dcp->notch_height],
 				     &dcp->panel.height_mm);
+		if (of_property_read_string_index(panel_np, "compatible", 0,
+						  &compatible))
+			compatible = NULL;
 		/* The most specific compatible names the panel for its EDID. */
-		if (iomfb_v14_7_base_edid(dcp) &&
-		    !of_property_read_string_index(panel_np, "compatible", 0, &compatible) &&
+		if (iomfb_v14_7_base_edid(dcp) && compatible &&
 		    dcp_panel_id_from_compatible(&dcp->panel.id, compatible))
 			dev_dbg(dev, "no EDID make and product in '%s'\n", compatible);
+		/*
+		 * Only this panel.  The backlight device's maximum is this
+		 * value, so 100% asks the firmware for DCP_J313_MAX_NITS.
+		 */
+		if (dcp_panel_is_j313(&dcp->panel.id, compatible) &&
+		    dcp->brightness.maximum > DCP_J313_MAX_NITS) {
+			dcp->brightness.maximum = DCP_J313_MAX_NITS;
+			if (dcp->brightness.nits > (int)DCP_J313_MAX_NITS)
+				dcp->brightness.nits = DCP_J313_MAX_NITS;
+			dev_info(dev, "capping panel backlight at %u nits\n",
+				 DCP_J313_MAX_NITS);
+		}
 
 		of_node_put(panel_np);
 		dcp->fixed_connector_type = DRM_MODE_CONNECTOR_eDP;

drivers/gpu/drm/apple/dcp_backlight.c

@@ -161,6 +161,11 @@ static int dcp_get_brightness(struct backlight_device *bd)
 		return ret;
 	}
 
+	if (dcp->brightness.nits < 0)
+		return 0;
+	if (bd->props.max_brightness > 0 &&
+	    dcp->brightness.nits > bd->props.max_brightness)
+		return bd->props.max_brightness;
 	return dcp->brightness.nits;
 }
 

drivers/gpu/drm/apple/iomfb_template.c

@@ -486,7 +486,12 @@ static void iomfb_cb_pr_publish(struct apple_dcp *dcp, struct iomfb_property *pr
 			break;
 #endif
 		if (dcp_has_panel(dcp)) {
-			dcp->brightness.nits = prop->value / dcp->brightness.scale;
+			u32 nits = prop->value / dcp->brightness.scale;
+
+			/* Firmware can report the old 420-nit scale above the cap. */
+			if (dcp->brightness.maximum && nits > dcp->brightness.maximum)
+				nits = dcp->brightness.maximum;
+			dcp->brightness.nits = nits;
 			/* notify backlight device of the initial brightness */
 			if (!dcp->brightness.bl_dev && dcp->brightness.maximum > 0)
 				schedule_work(&dcp->bl_register_wq);
@@ -2090,19 +2095,16 @@ dcpep_cb_get_tiling_state(struct apple_dcp *dcp,
 
 static u8 dcpep_cb_create_backlight_service(struct apple_dcp *dcp)
 {
-#if DCP_FW_VER >= DCP_FW_VERSION(26, 0, 0)
 	/*
-	 * H17P asks during start_ios_gated, before any mode is known, but
-	 * dcp_has_panel() only becomes true once the panel dimensions have been
-	 * parsed.  An internal panel always has a backlight, so answer for the
-	 * connector; answering false makes the firmware report that it could
-	 * not find the backlight service.
+	 * Firmware asks during start_ios_gated. On J313 the panel node is
+	 * read first, so width_mm is already set and dcp_has_panel() is
+	 * already true. Answering eDP as well does not change this return
+	 * value. DCP 13.5 still logs that it could not find the backlight
+	 * service, and writes still apply only after a modeset.
+	 * External displays are not eDP.
 	 */
 	return dcp_has_panel(dcp) ||
 	       dcp->connector_type == DRM_MODE_CONNECTOR_eDP;
-#else
-	return dcp_has_panel(dcp);
-#endif
 }
 
 TRAMPOLINE_VOID(trampoline_nop, dcpep_cb_nop);

drivers/gpu/drm/apple/systemep.c

@@ -74,6 +74,7 @@ static int powerlog_report(struct apple_epic_service *service, enum epic_subtype
 	struct dcp_parse_ctx parse_ctx;
 	struct apple_dcp *dcp = service->ep->dcp;
 	int ret;
+	u32 nits;
 
 	/* Later reports must not overwrite a latched hint or Linux's target. */
 	if (dcp_backlight_active(dcp))
@@ -110,7 +111,11 @@ static int powerlog_report(struct apple_epic_service *service, enum epic_subtype
 		return 0;
 	}
 
-	dcp->brightness.nits = mnits.millinits / 1000;
+	nits = mnits.millinits / 1000;
+	/* Firmware can report the old 420-nit scale above the cap. */
+	if (dcp->brightness.maximum && nits > dcp->brightness.maximum)
+		nits = dcp->brightness.maximum;
+	dcp->brightness.nits = nits;
 
 	return 0;
 }