hwmon: (pmbus/adm1266) Add Block process call

PmBus devices support Block Write-Block Read Process
Call described in SMBus specification v 2.0 with the
exception that Block writes and reads are permitted to
have up 255 data bytes instead of max 32 bytes (SMBus).

This patch adds Block WR process call support for ADM1266.
Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Link: https://lore.kernel.org/r/20200812142055.9213-3-alexandru.tachici@analog.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/Kconfig

@@ -28,6 +28,7 @@ config SENSORS_PMBUS
 
 config SENSORS_ADM1266
 	tristate "Analog Devices ADM1266 Sequencer"
+	select CRC8
 	help
 	  If you say yes here you get hardware monitoring support for Analog
 	  Devices ADM1266 Cascadable Super Sequencer.

drivers/hwmon/pmbus/adm1266.c

@@ -6,6 +6,7 @@
  * Copyright 2020 Analog Devices Inc.
  */
 
+#include <linux/crc8.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
@@ -13,11 +14,85 @@
 #include "pmbus.h"
 #include <linux/slab.h>
 
+#define ADM1266_PMBUS_BLOCK_MAX		255
+
 struct adm1266_data {
 	struct pmbus_driver_info info;
 	struct i2c_client *client;
+	struct mutex buf_mutex;
+	u8 write_buf[ADM1266_PMBUS_BLOCK_MAX + 1] ____cacheline_aligned;
+	u8 read_buf[ADM1266_PMBUS_BLOCK_MAX + 1] ____cacheline_aligned;
 };
 
+DECLARE_CRC8_TABLE(pmbus_crc_table);
+
+/*
+ * Different from Block Read as it sends data and waits for the slave to
+ * return a value dependent on that data. The protocol is simply a Write Block
+ * followed by a Read Block without the Read-Block command field and the
+ * Write-Block STOP bit.
+ */
+static int adm1266_pmbus_block_xfer(struct adm1266_data *data, u8 cmd, u8 w_len, u8 *data_w,
+				    u8 *data_r)
+{
+	struct i2c_client *client = data->client;
+	struct i2c_msg msgs[2] = {
+		{
+			.addr = client->addr,
+			.flags = I2C_M_DMA_SAFE,
+			.buf = data->write_buf,
+			.len = w_len + 2,
+		},
+		{
+			.addr = client->addr,
+			.flags = I2C_M_RD | I2C_M_DMA_SAFE,
+			.buf = data->read_buf,
+			.len = ADM1266_PMBUS_BLOCK_MAX + 2,
+		}
+	};
+	u8 addr;
+	u8 crc;
+	int ret;
+
+	mutex_lock(&data->buf_mutex);
+
+	msgs[0].buf[0] = cmd;
+	msgs[0].buf[1] = w_len;
+	memcpy(&msgs[0].buf[2], data_w, w_len);
+
+	ret = i2c_transfer(client->adapter, msgs, 2);
+	if (ret != 2) {
+		if (ret >= 0)
+			ret = -EPROTO;
+
+		mutex_unlock(&data->buf_mutex);
+
+		return ret;
+	}
+
+	if (client->flags & I2C_CLIENT_PEC) {
+		addr = i2c_8bit_addr_from_msg(&msgs[0]);
+		crc = crc8(pmbus_crc_table, &addr, 1, 0);
+		crc = crc8(pmbus_crc_table, msgs[0].buf,  msgs[0].len, crc);
+
+		addr = i2c_8bit_addr_from_msg(&msgs[1]);
+		crc = crc8(pmbus_crc_table, &addr, 1, crc);
+		crc = crc8(pmbus_crc_table, msgs[1].buf,  msgs[1].buf[0] + 1, crc);
+
+		if (crc != msgs[1].buf[msgs[1].buf[0] + 1]) {
+			mutex_unlock(&data->buf_mutex);
+			return -EBADMSG;
+		}
+	}
+
+	memcpy(data_r, &msgs[1].buf[1], msgs[1].buf[0]);
+
+	ret = msgs[1].buf[0];
+	mutex_unlock(&data->buf_mutex);
+
+	return ret;
+}
+
 static int adm1266_probe(struct i2c_client *client)
 {
 	struct adm1266_data *data;
@@ -33,6 +108,9 @@ static int adm1266_probe(struct i2c_client *client)
 	for (i = 0; i < data->info.pages; i++)
 		data->info.func[i] = PMBUS_HAVE_VOUT | PMBUS_HAVE_STATUS_VOUT;
 
+	crc8_populate_msb(pmbus_crc_table, 0x7);
+	mutex_init(&data->buf_mutex);
+
 	return pmbus_do_probe(client, &data->info);
 }