thunderbolt: Improve software receiver lane margining

USB4 specification defines the metadata needed to perform software
margining, as well as the necessary steps which include waiting for
dwell time.

- Add dwell_time attribute to set the wait time while performing
  margining and checking for link errors.
- Add error_counter attribute to configure error counter prior to
  margining test.
- Add voltage_time_offset attribute to set the voltage or time offset
  steps before performing the software margining test.
- Perform software margining test for dwell duration, break if there are
  link errors, stop the clocks and provide results.

Below is a minimalistic example how this can be used. Note these values
are just examples. The exact values in practice depend on host specific
capabilities and the type of measurement to be performed.

  # cd /sys/kernel/debug/thunderbolt/ROUTER/portX/margining/
  # echo software > mode
  # echo 400 > dwell_time
  # echo 1 > run

As usual the results attribute contains the results of a succesfull run.

Signed-off-by: R Kannappan <[email protected]>
Co-developed-by: Rene Sapiens <[email protected]>
Signed-off-by: Rene Sapiens <[email protected]>
Co-developed-by: Aapo Vienamo <[email protected]>
Signed-off-by: Aapo Vienamo <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>

Author: r-kannappan

drivers/thunderbolt/debugfs.c

@@ -9,6 +9,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/debugfs.h>
+#include <linux/delay.h>
 #include <linux/pm_runtime.h>
 #include <linux/uaccess.h>
 
@@ -34,6 +35,14 @@
 
 #define COUNTER_SET_LEN		3
 
+/*
+ * USB4 spec doesn't specify dwell range, the range of 100 ms to 500 ms
+ * probed to give good results.
+ */
+#define MIN_DWELL_TIME		100 /* ms */
+#define MAX_DWELL_TIME		500 /* ms */
+#define DWELL_SAMPLE_INTERVAL	10
+
 /* Sideband registers and their sizes as defined in the USB4 spec */
 struct sb_reg {
 	unsigned int reg;
@@ -399,6 +408,9 @@ static ssize_t retimer_sb_regs_write(struct file *file,
  *					range (in mV).
  * @time_steps: Number of time margin steps
  * @max_time_offset: Maximum time margin offset (in mUI)
+ * @voltage_time_offset: Offset for voltage / time for software margining
+ * @dwell_time: Dwell time for software margining (in ms)
+ * @error_counter: Error counter operation for software margining
  * @optional_voltage_offset_range: Enable optional extended voltage range
  * @software: %true if software margining is used instead of hardware
  * @time: %true if time margining is used instead of voltage
@@ -422,12 +434,33 @@ struct tb_margining {
 	unsigned int max_voltage_offset_optional_range;
 	unsigned int time_steps;
 	unsigned int max_time_offset;
+	unsigned int voltage_time_offset;
+	unsigned int dwell_time;
+	enum usb4_margin_sw_error_counter error_counter;
 	bool optional_voltage_offset_range;
 	bool software;
 	bool time;
 	bool right_high;
 };
 
+static int margining_modify_error_counter(struct tb_margining *margining,
+	u32 lanes, enum usb4_margin_sw_error_counter error_counter)
+{
+	struct usb4_port_margining_params params = { 0 };
+	struct tb_port *port = margining->port;
+	u32 result;
+
+	if (error_counter != USB4_MARGIN_SW_ERROR_COUNTER_CLEAR &&
+	    error_counter != USB4_MARGIN_SW_ERROR_COUNTER_STOP)
+		return -EOPNOTSUPP;
+
+	params.error_counter = error_counter;
+	params.lanes = lanes;
+
+	return usb4_port_sw_margin(port, margining->target, margining->index,
+				   &params, &result);
+}
+
 static bool supports_software(const struct tb_margining *margining)
 {
 	return margining->caps[0] & USB4_MARGIN_CAP_0_MODES_SW;
@@ -689,9 +722,165 @@ static int margining_lanes_show(struct seq_file *s, void *not_used)
 DEBUGFS_ATTR_RW(margining_lanes);
 
 static ssize_t
-margining_optional_voltage_offset_write(struct file *file,
-				   const char __user *user_buf,
-				   size_t count, loff_t *ppos)
+margining_voltage_time_offset_write(struct file *file,
+				    const char __user *user_buf,
+				    size_t count, loff_t *ppos)
+{
+	struct seq_file *s = file->private_data;
+	struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+	unsigned int max_margin;
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint_from_user(user_buf, count, 10, &val);
+	if (ret)
+		return ret;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		if (margining->time)
+			max_margin = margining->time_steps;
+		else
+			if (margining->optional_voltage_offset_range)
+				max_margin = margining->voltage_steps_optional_range;
+			else
+				max_margin = margining->voltage_steps;
+
+		margining->voltage_time_offset = clamp(val, 0, max_margin);
+	}
+
+	return count;
+}
+
+static int margining_voltage_time_offset_show(struct seq_file *s,
+					      void *not_used)
+{
+	const struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		seq_printf(s, "%d\n", margining->voltage_time_offset);
+	}
+
+	return 0;
+}
+DEBUGFS_ATTR_RW(margining_voltage_time_offset);
+
+static ssize_t
+margining_error_counter_write(struct file *file, const char __user *user_buf,
+			      size_t count, loff_t *ppos)
+{
+	enum usb4_margin_sw_error_counter error_counter;
+	struct seq_file *s = file->private_data;
+	struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+	char *buf;
+
+	buf = validate_and_copy_from_user(user_buf, &count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	buf[count - 1] = '\0';
+
+	if (!strcmp(buf, "nop"))
+		error_counter = USB4_MARGIN_SW_ERROR_COUNTER_NOP;
+	else if (!strcmp(buf, "clear"))
+		error_counter = USB4_MARGIN_SW_ERROR_COUNTER_CLEAR;
+	else if (!strcmp(buf, "start"))
+		error_counter = USB4_MARGIN_SW_ERROR_COUNTER_START;
+	else if (!strcmp(buf, "stop"))
+		error_counter = USB4_MARGIN_SW_ERROR_COUNTER_STOP;
+	else
+		return -EINVAL;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		margining->error_counter = error_counter;
+	}
+
+	return count;
+}
+
+static int margining_error_counter_show(struct seq_file *s, void *not_used)
+{
+	const struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		switch (margining->error_counter) {
+		case USB4_MARGIN_SW_ERROR_COUNTER_NOP:
+			seq_puts(s, "[nop] clear start stop\n");
+			break;
+		case USB4_MARGIN_SW_ERROR_COUNTER_CLEAR:
+			seq_puts(s, "nop [clear] start stop\n");
+			break;
+		case USB4_MARGIN_SW_ERROR_COUNTER_START:
+			seq_puts(s, "nop clear [start] stop\n");
+			break;
+		case USB4_MARGIN_SW_ERROR_COUNTER_STOP:
+			seq_puts(s, "nop clear start [stop]\n");
+			break;
+		}
+	}
+
+	return 0;
+}
+DEBUGFS_ATTR_RW(margining_error_counter);
+
+static ssize_t
+margining_dwell_time_write(struct file *file, const char __user *user_buf,
+			   size_t count, loff_t *ppos)
+{
+	struct seq_file *s = file->private_data;
+	struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint_from_user(user_buf, count, 10, &val);
+	if (ret)
+		return ret;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		margining->dwell_time = clamp(val, MIN_DWELL_TIME, MAX_DWELL_TIME);
+	}
+
+	return count;
+}
+
+static int margining_dwell_time_show(struct seq_file *s, void *not_used)
+{
+	struct tb_margining *margining = s->private;
+	struct tb *tb = margining->port->sw->tb;
+
+	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &tb->lock) {
+		if (!margining->software)
+			return -EOPNOTSUPP;
+
+		seq_printf(s, "%d\n", margining->dwell_time);
+	}
+
+	return 0;
+}
+DEBUGFS_ATTR_RW(margining_dwell_time);
+
+static ssize_t
+margining_optional_voltage_offset_write(struct file *file, const char __user *user_buf,
+					size_t count, loff_t *ppos)
 {
 	struct seq_file *s = file->private_data;
 	struct tb_margining *margining = s->private;
@@ -796,6 +985,51 @@ static int margining_mode_show(struct seq_file *s, void *not_used)
 }
 DEBUGFS_ATTR_RW(margining_mode);
 
+static int margining_run_sw(struct tb_margining *margining,
+			    struct usb4_port_margining_params *params)
+{
+	u32 nsamples = margining->dwell_time / DWELL_SAMPLE_INTERVAL;
+	int ret, i;
+
+	ret = usb4_port_sw_margin(margining->port, margining->target, margining->index,
+				  params, margining->results);
+	if (ret)
+		goto out_stop;
+
+	for (i = 0; i <= nsamples; i++) {
+		u32 errors = 0;
+
+		ret = usb4_port_sw_margin_errors(margining->port, margining->target,
+						 margining->index, &margining->results[1]);
+		if (ret)
+			break;
+
+		if (margining->lanes == USB4_MARGIN_SW_LANE_0)
+			errors = FIELD_GET(USB4_MARGIN_SW_ERR_COUNTER_LANE_0_MASK,
+					   margining->results[1]);
+		else if (margining->lanes == USB4_MARGIN_SW_LANE_1)
+			errors = FIELD_GET(USB4_MARGIN_SW_ERR_COUNTER_LANE_1_MASK,
+					   margining->results[1]);
+		else if (margining->lanes == USB4_MARGIN_SW_ALL_LANES)
+			errors = margining->results[1];
+
+		/* Any errors stop the test */
+		if (errors)
+			break;
+
+		fsleep(DWELL_SAMPLE_INTERVAL * USEC_PER_MSEC);
+	}
+
+out_stop:
+	/*
+	 * Stop the counters but don't clear them to allow the
+	 * different error counter configurations.
+	 */
+	margining_modify_error_counter(margining, margining->lanes,
+				       USB4_MARGIN_SW_ERROR_COUNTER_STOP);
+	return ret;
+}
+
 static int margining_run_write(void *data, u64 val)
 {
 	struct tb_margining *margining = data;
@@ -836,11 +1070,15 @@ static int margining_run_write(void *data, u64 val)
 		clx = ret;
 	}
 
+	/* Clear the results */
+	memset(margining->results, 0, sizeof(margining->results));
+
 	if (margining->software) {
 		struct usb4_port_margining_params params = {
 			.error_counter = USB4_MARGIN_SW_ERROR_COUNTER_CLEAR,
 			.lanes = margining->lanes,
 			.time = margining->time,
+			.voltage_time_offset = margining->voltage_time_offset,
 			.right_high = margining->right_high,
 			.optional_voltage_offset_range = margining->optional_voltage_offset_range,
 		};
@@ -850,14 +1088,7 @@ static int margining_run_write(void *data, u64 val)
 			    margining->time ? "time" : "voltage", dev_name(dev),
 			    margining->lanes);
 
-		ret = usb4_port_sw_margin(port, margining->target, margining->index, &params,
-					  &margining->results[0]);
-		if (ret)
-			goto out_clx;
-
-		ret = usb4_port_sw_margin_errors(port, margining->target,
-						 margining->index,
-						 &margining->results[0]);
+		ret = margining_run_sw(margining, &params);
 	} else {
 		struct usb4_port_margining_params params = {
 			.ber_level = margining->ber_level,
@@ -867,10 +1098,6 @@ static int margining_run_write(void *data, u64 val)
 			.optional_voltage_offset_range = margining->optional_voltage_offset_range,
 		};
 
-		/* Clear the results */
-		margining->results[0] = 0;
-		margining->results[1] = 0;
-
 		tb_port_dbg(port,
 			    "running hardware %s lane margining for %s lanes %u\n",
 			    margining->time ? "time" : "voltage", dev_name(dev),
@@ -880,7 +1107,6 @@ static int margining_run_write(void *data, u64 val)
 					  margining->results);
 	}
 
-out_clx:
 	if (down_sw)
 		tb_switch_clx_enable(down_sw, clx);
 out_unlock:
@@ -909,6 +1135,13 @@ static ssize_t margining_results_write(struct file *file,
 	margining->results[0] = 0;
 	margining->results[1] = 0;
 
+	if (margining->software) {
+		/* Clear the error counters */
+		margining_modify_error_counter(margining,
+					       USB4_MARGIN_SW_ALL_LANES,
+					       USB4_MARGIN_SW_ERROR_COUNTER_CLEAR);
+	}
+
 	mutex_unlock(&tb->lock);
 	return count;
 }
@@ -998,6 +1231,24 @@ static int margining_results_show(struct seq_file *s, void *not_used)
 				voltage_margin_show(s, margining, val);
 			}
 		}
+	} else {
+		u32 lane_errors, result;
+
+		seq_printf(s, "0x%08x\n", margining->results[1]);
+		result = FIELD_GET(USB4_MARGIN_SW_LANES_MASK, margining->results[0]);
+
+		if (result == USB4_MARGIN_SW_LANE_0 ||
+		    result == USB4_MARGIN_SW_ALL_LANES) {
+			lane_errors = FIELD_GET(USB4_MARGIN_SW_ERR_COUNTER_LANE_0_MASK,
+						margining->results[1]);
+			seq_printf(s, "# lane 0 errors: %u\n", lane_errors);
+		}
+		if (result == USB4_MARGIN_SW_LANE_1 ||
+		    result == USB4_MARGIN_SW_ALL_LANES) {
+			lane_errors = FIELD_GET(USB4_MARGIN_SW_ERR_COUNTER_LANE_1_MASK,
+						margining->results[1]);
+			seq_printf(s, "# lane 1 errors: %u\n", lane_errors);
+		}
 	}
 
 	mutex_unlock(&tb->lock);
@@ -1211,9 +1462,21 @@ static struct tb_margining *margining_alloc(struct tb_port *port,
 		debugfs_create_file("margin", 0600, dir, margining,
 				    &margining_margin_fops);
 
+	margining->error_counter = USB4_MARGIN_SW_ERROR_COUNTER_CLEAR;
+	margining->dwell_time = MIN_DWELL_TIME;
+
 	if (supports_optional_voltage_offset_range(margining))
 		debugfs_create_file("optional_voltage_offset", DEBUGFS_MODE, dir, margining,
 				    &margining_optional_voltage_offset_fops);
+
+	if (supports_software(margining)) {
+		debugfs_create_file("voltage_time_offset", DEBUGFS_MODE, dir, margining,
+				    &margining_voltage_time_offset_fops);
+		debugfs_create_file("error_counter", DEBUGFS_MODE, dir, margining,
+				    &margining_error_counter_fops);
+		debugfs_create_file("dwell_time", DEBUGFS_MODE, dir, margining,
+				    &margining_dwell_time_fops);
+	}
 	return margining;
 }