2 files changed, 108 insertions, 12 deletions
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
index e79ac1e2c460..35ca732f7ffe 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
@@ -720,16 +720,49 @@ int connector_debugfs_init(struct amdgpu_dm_connector *connector)
 	return 0;
 }
 
+/*
+ * Writes DTN log state to the user supplied buffer.
+ * Example usage: cat /sys/kernel/debug/dri/0/amdgpu_dm_dtn_log
+ */
 static ssize_t dtn_log_read(
 	struct file *f,
 	char __user *buf,
 	size_t size,
 	loff_t *pos)
 {
-	/* TODO: Write log output to the user supplied buffer. */
-	return 0;
+	struct amdgpu_device *adev = file_inode(f)->i_private;
+	struct dc *dc = adev->dm.dc;
+	struct dc_log_buffer_ctx log_ctx = { 0 };
+	ssize_t result = 0;
+
+	if (!buf || !size)
+		return -EINVAL;
+
+	if (!dc->hwss.log_hw_state)
+		return 0;
+
+	dc->hwss.log_hw_state(dc, &log_ctx);
+
+	if (*pos < log_ctx.pos) {
+		size_t to_copy = log_ctx.pos - *pos;
+
+		to_copy = min(to_copy, size);
+
+		if (!copy_to_user(buf, log_ctx.buf + *pos, to_copy)) {
+			*pos += to_copy;
+			result = to_copy;
+		}
+	}
+
+	kfree(log_ctx.buf);
+
+	return result;
 }
 
+/*
+ * Writes DTN log state to dmesg when triggered via a write.
+ * Example usage: echo 1 > /sys/kernel/debug/dri/0/amdgpu_dm_dtn_log
+ */
 static ssize_t dtn_log_write(
 	struct file *f,
 	const char __user *buf,
@@ -744,7 +777,7 @@ static ssize_t dtn_log_write(
 		return 0;
 
 	if (dc->hwss.log_hw_state)
-		dc->hwss.log_hw_state(dc);
+		dc->hwss.log_hw_state(dc, NULL);
 
 	return size;
 }
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
index 86b63ce1dbf6..39997d977efb 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
@@ -335,28 +335,91 @@ bool dm_helpers_dp_mst_send_payload_allocation(
 	return true;
 }
 
-void dm_dtn_log_begin(struct dc_context *ctx)
+void dm_dtn_log_begin(struct dc_context *ctx,
+	struct dc_log_buffer_ctx *log_ctx)
 {
-	pr_info("[dtn begin]\n");
+	static const char msg[] = "[dtn begin]\n";
+
+	if (!log_ctx) {
+		pr_info("%s", msg);
+		return;
+	}
+
+	dm_dtn_log_append_v(ctx, log_ctx, "%s", msg);
 }
 
 void dm_dtn_log_append_v(struct dc_context *ctx,
-		const char *msg, ...)
+	struct dc_log_buffer_ctx *log_ctx,
+	const char *msg, ...)
 {
-	struct va_format vaf;
 	va_list args;
+	size_t total;
+	int n;
+
+	if (!log_ctx) {
+		/* No context, redirect to dmesg. */
+		struct va_format vaf;
+
+		vaf.fmt = msg;
+		vaf.va = &args;
+
+		va_start(args, msg);
+		pr_info("%pV", &vaf);
+		va_end(args);
 
+		return;
+	}
+
+	/* Measure the output. */
 	va_start(args, msg);
-	vaf.fmt = msg;
-	vaf.va = &args;
+	n = vsnprintf(NULL, 0, msg, args);
+	va_end(args);
+
+	if (n <= 0)
+		return;
+
+	/* Reallocate the string buffer as needed. */
+	total = log_ctx->pos + n + 1;
 
-	pr_info("%pV", &vaf);
+	if (total > log_ctx->size) {
+		char *buf = (char *)kvcalloc(total, sizeof(char), GFP_KERNEL);
+
+		if (buf) {
+			memcpy(buf, log_ctx->buf, log_ctx->pos);
+			kfree(log_ctx->buf);
+
+			log_ctx->buf = buf;
+			log_ctx->size = total;
+		}
+	}
+
+	if (!log_ctx->buf)
+		return;
+
+	/* Write the formatted string to the log buffer. */
+	va_start(args, msg);
+	n = vscnprintf(
+		log_ctx->buf + log_ctx->pos,
+		log_ctx->size - log_ctx->pos,
+		msg,
+		args);
 	va_end(args);
+
+	if (n > 0)
+		log_ctx->pos += n;
 }
 
-void dm_dtn_log_end(struct dc_context *ctx)
+void dm_dtn_log_end(struct dc_context *ctx,
+	struct dc_log_buffer_ctx *log_ctx)
 {
-	pr_info("[dtn end]\n");
+	static const char msg[] = "[dtn end]\n";
+
+	if (!log_ctx) {
+		pr_info("%s", msg);
+		return;
+	}
+
+	dm_dtn_log_append_v(ctx, log_ctx, "%s", msg);
 }
 
 bool dm_helpers_dp_mst_start_top_mgr(