drm/amd/display: Add debugfs entry for dsc passthrough

[Why & How]
Add debugfs entry to force dsc decoding at PCON when DSC capable
external RX is connected. In such case, it is free to test DSC
decoding at external RX or at PCON.
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -456,6 +456,7 @@ struct dsc_preferred_settings {
 	uint32_t dsc_num_slices_v;
 	uint32_t dsc_num_slices_h;
 	uint32_t dsc_bits_per_pixel;
+	bool dsc_force_disable_passthrough;
 };
 
 struct amdgpu_dm_connector {

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

@@ -887,6 +887,47 @@ static int output_bpc_show(struct seq_file *m, void *data)
 	return res;
 }
 
+/*
+ * Example usage:
+ * Disable dsc passthrough, i.e.,: have dsc decoding at converver, not external RX
+ *   echo 1 /sys/kernel/debug/dri/0/DP-1/dsc_disable_passthrough
+ * Enable dsc passthrough, i.e.,: have dsc passthrough to external RX
+ *   echo 0 /sys/kernel/debug/dri/0/DP-1/dsc_disable_passthrough
+ */
+static ssize_t dp_dsc_passthrough_set(struct file *f, const char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	struct amdgpu_dm_connector *aconnector = file_inode(f)->i_private;
+	char *wr_buf = NULL;
+	uint32_t wr_buf_size = 42;
+	int max_param_num = 1;
+	long param;
+	uint8_t param_nums = 0;
+
+	if (size == 0)
+		return -EINVAL;
+
+	wr_buf = kcalloc(wr_buf_size, sizeof(char), GFP_KERNEL);
+
+	if (!wr_buf) {
+		DRM_DEBUG_DRIVER("no memory to allocate write buffer\n");
+		return -ENOSPC;
+	}
+
+	if (parse_write_buffer_into_params(wr_buf, size,
+					   &param, buf,
+					   max_param_num,
+					   &param_nums)) {
+		kfree(wr_buf);
+		return -EINVAL;
+	}
+
+	aconnector->dsc_settings.dsc_force_disable_passthrough = param;
+
+	kfree(wr_buf);
+	return 0;
+}
+
 #ifdef CONFIG_DRM_AMD_DC_HDCP
 /*
  * Returns the HDCP capability of the Display (1.4 for now).
@@ -2535,6 +2576,12 @@ static const struct file_operations dp_max_bpc_debugfs_fops = {
 	.llseek = default_llseek
 };
 
+static const struct file_operations dp_dsc_disable_passthrough_debugfs_fops = {
+	.owner = THIS_MODULE,
+	.write = dp_dsc_passthrough_set,
+	.llseek = default_llseek
+};
+
 static const struct {
 	char *name;
 	const struct file_operations *fops;
@@ -2559,7 +2606,8 @@ static const struct {
 		{"dsc_chunk_size", &dp_dsc_chunk_size_debugfs_fops},
 		{"dsc_slice_bpg", &dp_dsc_slice_bpg_offset_debugfs_fops},
 		{"dp_dsc_fec_support", &dp_dsc_fec_support_fops},
-		{"max_bpc", &dp_max_bpc_debugfs_fops}
+		{"max_bpc", &dp_max_bpc_debugfs_fops},
+		{"dsc_disable_passthrough", &dp_dsc_disable_passthrough_debugfs_fops},
 };
 
 #ifdef CONFIG_DRM_AMD_DC_HDCP