drm/amd/display: Add support for hw_state logging via debugfs

[Why]

We have logging methods for printing hardware state for newer ASICs
but no way to trigger the log output.

[How]

Add support for triggering the output via writing to a debugfs file
entry. Log output currently goes into dmesg for convenience, but
accessing via a read should be possible later.
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Jordan Lazare <Jordan.Lazare@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -480,6 +480,11 @@ static int amdgpu_dm_init(struct amdgpu_device *adev)
 		goto error;
 	}
 
+#if defined(CONFIG_DEBUG_FS)
+	if (dtn_debugfs_init(adev))
+		DRM_ERROR("amdgpu: failed initialize dtn debugfs support.\n");
+#endif
+
 	DRM_DEBUG_DRIVER("KMS initialized.\n");
 
 	return 0;

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -720,3 +720,56 @@ int connector_debugfs_init(struct amdgpu_dm_connector *connector)
 	return 0;
 }
 
+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;
+}
+
+static ssize_t dtn_log_write(
+	struct file *f,
+	const char __user *buf,
+	size_t size,
+	loff_t *pos)
+{
+	struct amdgpu_device *adev = file_inode(f)->i_private;
+	struct dc *dc = adev->dm.dc;
+
+	/* Write triggers log output via dmesg. */
+	if (size == 0)
+		return 0;
+
+	if (dc->hwss.log_hw_state)
+		dc->hwss.log_hw_state(dc);
+
+	return size;
+}
+
+int dtn_debugfs_init(struct amdgpu_device *adev)
+{
+	static const struct file_operations dtn_log_fops = {
+		.owner = THIS_MODULE,
+		.read = dtn_log_read,
+		.write = dtn_log_write,
+		.llseek = default_llseek
+	};
+
+	struct drm_minor *minor = adev->ddev->primary;
+	struct dentry *root = minor->debugfs_root;
+
+	struct dentry *ent = debugfs_create_file(
+		"amdgpu_dm_dtn_log",
+		0644,
+		root,
+		adev,
+		&dtn_log_fops);
+
+	if (IS_ERR(ent))
+		return PTR_ERR(ent);
+
+	return 0;
+}

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.h

@@ -30,5 +30,6 @@
 #include "amdgpu_dm.h"
 
 int connector_debugfs_init(struct amdgpu_dm_connector *connector);
+int dtn_debugfs_init(struct amdgpu_device *adev);
 
 #endif

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -336,14 +336,28 @@ bool dm_helpers_dp_mst_send_payload_allocation(
 }
 
 void dm_dtn_log_begin(struct dc_context *ctx)
-{}
+{
+	pr_info("[dtn begin]\n");
+}
 
 void dm_dtn_log_append_v(struct dc_context *ctx,
-		const char *pMsg, ...)
-{}
+		const char *msg, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, msg);
+	vaf.fmt = msg;
+	vaf.va = &args;
+
+	pr_info("%pV", &vaf);
+	va_end(args);
+}
 
 void dm_dtn_log_end(struct dc_context *ctx)
-{}
+{
+	pr_info("[dtn end]\n");
+}
 
 bool dm_helpers_dp_mst_start_top_mgr(
 		struct dc_context *ctx,