hwmon: (pmbus) Introduce page_change_delay

We have some buggy pmbus devices that require a delay after performing a
page change operation before trying to issue more commands to the
device.

This allows for a configurable delay after page changes, but not
affecting other read or write operations.

This makes a slight behavioral tweak to the existing delay logic, where
it considers the longest of delays between operations, instead of always
chosing the write delay over the access delay.

Signed-off-by: William A. Kennington III <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/pmbus/pmbus.h

···
 	 */
 	int access_delay;		/* in microseconds */
 	int write_delay;		/* in microseconds */
+	int page_change_delay;		/* in microseconds */
 };
 
 /* Regulator ops */

drivers/hwmon/pmbus/pmbus_core.c

···
 #define PMBUS_ATTR_ALLOC_SIZE	32
 #define PMBUS_NAME_SIZE		24
 
+/*
+ * The type of operation used for picking the delay between
+ * successive pmbus operations.
+ */
+#define PMBUS_OP_WRITE		BIT(0)
+#define PMBUS_OP_PAGE_CHANGE	BIT(1)
+
 static int wp = -1;
 module_param(wp, int, 0444);
 
···
 
 	int vout_low[PMBUS_PAGES];	/* voltage low margin */
 	int vout_high[PMBUS_PAGES];	/* voltage high margin */
-	ktime_t write_time;		/* Last SMBUS write timestamp */
-	ktime_t access_time;		/* Last SMBUS access timestamp */
+
+	ktime_t next_access_backoff;	/* Wait until at least this time */
 };
 
 struct pmbus_debugfs_entry {
···
 static void pmbus_wait(struct i2c_client *client)
 {
 	struct pmbus_data *data = i2c_get_clientdata(client);
-	const struct pmbus_driver_info *info = data->info;
-	s64 delta;
+	s64 delay = ktime_us_delta(data->next_access_backoff, ktime_get());
 
-	if (info->access_delay) {
-		delta = ktime_us_delta(ktime_get(), data->access_time);
-
-		if (delta < info->access_delay)
-			fsleep(info->access_delay - delta);
-	} else if (info->write_delay) {
-		delta = ktime_us_delta(ktime_get(), data->write_time);
-
-		if (delta < info->write_delay)
-			fsleep(info->write_delay - delta);
-	}
+	if (delay > 0)
+		fsleep(delay);
 }
 
-/* Sets the last accessed timestamp for pmbus_wait */
-static void pmbus_update_ts(struct i2c_client *client, bool write_op)
+/* Sets the last operation timestamp for pmbus_wait */
+static void pmbus_update_ts(struct i2c_client *client, int op)
 {
 	struct pmbus_data *data = i2c_get_clientdata(client);
 	const struct pmbus_driver_info *info = data->info;
+	int delay = info->access_delay;
 
-	if (info->access_delay)
-		data->access_time = ktime_get();
-	else if (info->write_delay && write_op)
-		data->write_time = ktime_get();
+	if (op & PMBUS_OP_WRITE)
+		delay = max(delay, info->write_delay);
+	if (op & PMBUS_OP_PAGE_CHANGE)
+		delay = max(delay, info->page_change_delay);
+
+	if (delay > 0)
+		data->next_access_backoff = ktime_add_us(ktime_get(), delay);
 }
 
 int pmbus_set_page(struct i2c_client *client, int page, int phase)
···
 	    data->info->pages > 1 && page != data->currpage) {
 		pmbus_wait(client);
 		rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
-		pmbus_update_ts(client, true);
+		pmbus_update_ts(client, PMBUS_OP_WRITE | PMBUS_OP_PAGE_CHANGE);
 		if (rv < 0)
 			return rv;
 
 		pmbus_wait(client);
 		rv = i2c_smbus_read_byte_data(client, PMBUS_PAGE);
-		pmbus_update_ts(client, false);
+		pmbus_update_ts(client, 0);
 		if (rv < 0)
 			return rv;
 
···
 		pmbus_wait(client);
 		rv = i2c_smbus_write_byte_data(client, PMBUS_PHASE,
 					       phase);
-		pmbus_update_ts(client, true);
+		pmbus_update_ts(client, PMBUS_OP_WRITE);
 		if (rv)
 			return rv;
 	}
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_write_byte(client, value);
-	pmbus_update_ts(client, true);
+	pmbus_update_ts(client, PMBUS_OP_WRITE);
 
 	return rv;
 }
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_write_word_data(client, reg, word);
-	pmbus_update_ts(client, true);
+	pmbus_update_ts(client, PMBUS_OP_WRITE);
 
 	return rv;
 }
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_read_word_data(client, reg);
-	pmbus_update_ts(client, false);
+	pmbus_update_ts(client, 0);
 
 	return rv;
 }
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_read_byte_data(client, reg);
-	pmbus_update_ts(client, false);
+	pmbus_update_ts(client, 0);
 
 	return rv;
 }
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_write_byte_data(client, reg, value);
-	pmbus_update_ts(client, true);
+	pmbus_update_ts(client, PMBUS_OP_WRITE);
 
 	return rv;
 }
···
 
 	pmbus_wait(client);
 	rv = i2c_smbus_read_block_data(client, reg, data_buf);
-	pmbus_update_ts(client, false);
+	pmbus_update_ts(client, 0);
 
 	return rv;
 }
···
 	rv = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
 			    I2C_SMBUS_WRITE, PMBUS_COEFFICIENTS,
 			    I2C_SMBUS_BLOCK_PROC_CALL, &data);
-	pmbus_update_ts(client, true);
+	pmbus_update_ts(client, PMBUS_OP_WRITE);
 
 	if (rv < 0)
 		return rv;
···
 	if (!(data->flags & PMBUS_NO_CAPABILITY)) {
 		pmbus_wait(client);
 		ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
-		pmbus_update_ts(client, false);
+		pmbus_update_ts(client, 0);
 
 		if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK)) {
 			if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_PEC))
···
 	data->read_status = pmbus_read_status_word;
 	pmbus_wait(client);
 	ret = i2c_smbus_read_word_data(client, PMBUS_STATUS_WORD);
-	pmbus_update_ts(client, false);
+	pmbus_update_ts(client, 0);
 
 	if (ret < 0 || ret == 0xffff) {
 		data->read_status = pmbus_read_status_byte;
 		pmbus_wait(client);
 		ret = i2c_smbus_read_byte_data(client, PMBUS_STATUS_BYTE);
-		pmbus_update_ts(client, false);
+		pmbus_update_ts(client, 0);
 
 		if (ret < 0 || ret == 0xff) {
 			dev_err(dev, "PMBus status register not found\n");