drm: apple: epic: systemep: Parse "mNits" log events

The 13.5 firmware has stopped updating the NITS property on backlight
brightness changes. Parse system log events instead which report
backlight's brightness in millinits.
Fixes the backlight device's "actual_brightness" property used by the
systemd backlight service to save and restore brightness.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/gpu/drm/apple/parser.c

@@ -983,3 +983,51 @@ int parse_sound_mode(struct dcp_parse_ctx *handle,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(parse_sound_mode);
+
+int parse_system_log_mnits(struct dcp_parse_ctx *handle, struct dcp_system_ev_mnits *entry)
+{
+	struct iterator it;
+	int ret;
+	s64 mnits = -1;
+	s64 idac = -1;
+	s64 timestamp = -1;
+	bool type_match = false;
+
+	dcp_parse_foreach_in_dict(handle, it) {
+		char *key = parse_string(it.handle);
+		if (IS_ERR(key)) {
+			ret = PTR_ERR(key);
+		} else if (!strcmp(key, "mNits")) {
+			ret = parse_int(it.handle, &mnits);
+		} else if (!strcmp(key, "iDAC")) {
+			ret = parse_int(it.handle, &idac);
+		} else if (!strcmp(key, "logEvent")) {
+			const char * value = parse_string(it.handle);
+			if (!IS_ERR_OR_NULL(value)) {
+				type_match = strcmp(value, "Display (Event Forward)") == 0;
+				kfree(value);
+			}
+		} else if (!strcmp(key, "timestamp")) {
+			ret = parse_int(it.handle, &timestamp);
+		} else {
+			skip(it.handle);
+		}
+
+		if (!IS_ERR_OR_NULL(key))
+			kfree(key);
+
+		if (ret) {
+			pr_err("dcp parser: failed to parse mNits sys event\n");
+			return ret;
+		}
+	}
+
+	if (!type_match ||  mnits < 0 || idac < 0 || timestamp < 0)
+		return -EINVAL;
+
+	entry->millinits = mnits;
+	entry->idac = idac;
+	entry->timestamp = timestamp;
+
+	return 0;
+}

drivers/gpu/drm/apple/parser.h

@@ -126,4 +126,13 @@ int parse_sound_mode(struct dcp_parse_ctx *handle,
 		     struct snd_pcm_chmap_elem *chmap,
 		     struct dcp_sound_cookie *cookie);
 
+struct dcp_system_ev_mnits {
+	u32 timestamp;
+	u32 millinits;
+	u32 idac;
+};
+
+int parse_system_log_mnits(struct dcp_parse_ctx *handle,
+			   struct dcp_system_ev_mnits *entry);
+
 #endif

drivers/gpu/drm/apple/systemep.c

@@ -5,6 +5,7 @@
 
 #include "afk.h"
 #include "dcp.h"
+#include "parser.h"
 
 static bool enable_verbose_logging;
 module_param(enable_verbose_logging, bool, 0644);
@@ -66,6 +67,41 @@ static void powerlog_init(struct apple_epic_service *service, const char *name,
 {
 }
 
+static int powerlog_report(struct apple_epic_service *service, enum epic_subtype type,
+			 const void *data, size_t data_size)
+{
+	struct dcp_system_ev_mnits mnits;
+	struct dcp_parse_ctx parse_ctx;
+	struct apple_dcp *dcp = service->ep->dcp;
+	int ret;
+
+	dev_dbg(dcp->dev, "systemep[ch:%u]: report type:%02x len:%zu\n",
+		service->channel, type, data_size);
+
+	if (type != EPIC_SUBTYPE_STD_SERVICE)
+		return 0;
+
+	ret = parse(data, data_size, &parse_ctx);
+	if (ret) {
+		dev_warn(service->ep->dcp->dev, "systemep: failed to parse report: %d\n", ret);
+		return ret;
+	}
+
+	ret = parse_system_log_mnits(&parse_ctx, &mnits);
+	if (ret) {
+		/* ignore parse errors in the case dcp sends unknown log events */
+		dev_dbg(dcp->dev, "systemep: failed to parse mNits event: %d\n", ret);
+		return 0;
+	}
+
+	dev_dbg(dcp->dev, "systemep: mNits event: Nits: %u.%03u, iDAC: %u\n",
+		mnits.millinits / 1000, mnits.millinits % 1000, mnits.idac);
+
+	dcp->brightness.nits = mnits.millinits / 1000;
+
+	return 0;
+}
+
 static const struct apple_epic_service_ops systemep_ops[] = {
 	{
 		.name = "system",
@@ -74,6 +110,7 @@ static const struct apple_epic_service_ops systemep_ops[] = {
 	{
 		.name = "powerlog-service",
 		.init = powerlog_init,
+		.report = powerlog_report,
 	},
 	{}
 };