drm/amd/display: Add debugfs dpcd interface

[Why]
We need arbitrary read/write over DP AUX DPCD
for debugging

[How]
Three debugfs entries

Set the target address by writing to
"aux_dpcd_address"
(The first four bytes written are used)

Set the transaction size in bytes by writing to
"aux_dpcd_size"
(The first four bytes written are used)

Start a transaction by reading/writing
"aux_dpcd_data"

Do note: there is no concerrency protection at all
Accessing these entries in quick succession can lead
to strange behaviour

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -4395,6 +4395,8 @@ static int amdgpu_dm_connector_init(struct amdgpu_display_manager *dm,
 		DRM_ERROR("Failed to create debugfs for connector");
 		goto out_free;
 	}
+	aconnector->debugfs_dpcd_address = 0;
+	aconnector->debugfs_dpcd_size = 0;
 #endif
 
 	if (connector_type == DRM_MODE_CONNECTOR_DisplayPort

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

@@ -238,6 +238,10 @@ struct amdgpu_dm_connector {
 	struct mutex hpd_lock;
 
 	bool fake_enable;
+#ifdef CONFIG_DEBUG_FS
+	uint32_t debugfs_dpcd_address;
+	uint32_t debugfs_dpcd_size;
+#endif
 };
 
 #define to_amdgpu_dm_connector(x) container_of(x, struct amdgpu_dm_connector, base)

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

@@ -29,6 +29,7 @@
 #include "amdgpu.h"
 #include "amdgpu_dm.h"
 #include "amdgpu_dm_debugfs.h"
+#include "dm_helpers.h"
 
 /* function description
  * get/ set DP configuration: lane_count, link_rate, spread_spectrum
@@ -731,6 +732,88 @@ static ssize_t dp_sdp_message_debugfs_write(struct file *f, const char __user *b
 
 DEFINE_SHOW_ATTRIBUTE(vrr_range);
 
+static ssize_t dp_dpcd_address_write(struct file *f, const char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	int r;
+	struct amdgpu_dm_connector *connector = file_inode(f)->i_private;
+
+	if (size < sizeof(connector->debugfs_dpcd_address))
+		return 0;
+
+	r = copy_from_user(&connector->debugfs_dpcd_address,
+			buf, sizeof(connector->debugfs_dpcd_address));
+
+	return size - r;
+}
+
+static ssize_t dp_dpcd_size_write(struct file *f, const char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	int r;
+	struct amdgpu_dm_connector *connector = file_inode(f)->i_private;
+
+	if (size < sizeof(connector->debugfs_dpcd_size))
+		return 0;
+
+	r = copy_from_user(&connector->debugfs_dpcd_size,
+			buf, sizeof(connector->debugfs_dpcd_size));
+
+	if (connector->debugfs_dpcd_size > 256)
+		connector->debugfs_dpcd_size = 0;
+
+	return size - r;
+}
+
+static ssize_t dp_dpcd_data_write(struct file *f, const char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	int r;
+	char *data;
+	struct amdgpu_dm_connector *connector = file_inode(f)->i_private;
+	struct dc_link *link = connector->dc_link;
+	uint32_t write_size = connector->debugfs_dpcd_size;
+
+	if (size < write_size)
+		return 0;
+
+	data = kzalloc(write_size, GFP_KERNEL);
+	if (!data)
+		return 0;
+
+	r = copy_from_user(data, buf, write_size);
+
+	dm_helpers_dp_write_dpcd(link->ctx, link,
+			connector->debugfs_dpcd_address, data, write_size - r);
+	kfree(data);
+	return write_size - r;
+}
+
+static ssize_t dp_dpcd_data_read(struct file *f, char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	int r;
+	char *data;
+	struct amdgpu_dm_connector *connector = file_inode(f)->i_private;
+	struct dc_link *link = connector->dc_link;
+	uint32_t read_size = connector->debugfs_dpcd_size;
+
+	if (size < read_size)
+		return 0;
+
+	data = kzalloc(read_size, GFP_KERNEL);
+	if (!data)
+		return 0;
+
+	dm_helpers_dp_read_dpcd(link->ctx, link,
+			connector->debugfs_dpcd_address, data, read_size);
+
+	r = copy_to_user(buf, data, read_size);
+
+	kfree(data);
+	return read_size - r;
+}
+
 static const struct file_operations dp_link_settings_debugfs_fops = {
 	.owner = THIS_MODULE,
 	.read = dp_link_settings_read,
@@ -757,6 +840,25 @@ static const struct file_operations sdp_message_fops = {
 	.llseek = default_llseek
 };
 
+static const struct file_operations dp_dpcd_address_debugfs_fops = {
+	.owner = THIS_MODULE,
+	.write = dp_dpcd_address_write,
+	.llseek = default_llseek
+};
+
+static const struct file_operations dp_dpcd_size_debugfs_fops = {
+	.owner = THIS_MODULE,
+	.write = dp_dpcd_size_write,
+	.llseek = default_llseek
+};
+
+static const struct file_operations dp_dpcd_data_debugfs_fops = {
+	.owner = THIS_MODULE,
+	.read = dp_dpcd_data_read,
+	.write = dp_dpcd_data_write,
+	.llseek = default_llseek
+};
+
 static const struct {
 	char *name;
 	const struct file_operations *fops;
@@ -765,7 +867,10 @@ static const struct {
 		{"phy_settings", &dp_phy_settings_debugfs_fop},
 		{"test_pattern", &dp_phy_test_pattern_fops},
 		{"vrr_range", &vrr_range_fops},
-		{"sdp_message", &sdp_message_fops}
+		{"sdp_message", &sdp_message_fops},
+		{"aux_dpcd_address", &dp_dpcd_address_debugfs_fops},
+		{"aux_dpcd_size", &dp_dpcd_size_debugfs_fops},
+		{"aux_dpcd_data", &dp_dpcd_data_debugfs_fops}
 };
 
 int connector_debugfs_init(struct amdgpu_dm_connector *connector)