mfd: cros_ec: Use a zero-length array for command data

Commit 1b84f2a4cd4a ("mfd: cros_ec: Use fixed size arrays to transfer
data with the EC") modified the struct cros_ec_command fields to not
use pointers for the input and output buffers and use fixed length
arrays instead.

This change was made because the cros_ec ioctl API uses that struct
cros_ec_command to allow user-space to send commands to the EC and
to get data from the EC. So using pointers made the API not 64-bit
safe. Unfortunately this approach was not flexible enough for all
the use-cases since there may be a need to send larger commands
on newer versions of the EC command protocol.

So to avoid to choose a constant length that it may be too big for
most commands and thus wasting memory and CPU cycles on copy from
and to user-space or having a size that is too small for some big
commands, use a zero-length array that is both 64-bit safe and
flexible. The same buffer is used for both output and input data
so the maximum of these values should be used to allocate it.

Suggested-by: Gwendal Grignou <[e-mail]>
Signed-off-by: Javier Martinez Canillas <[e-mail]>
Tested-by: Heiko Stuebner <[e-mail]>
Acked-by: Lee Jones <[e-mail]>
Acked-by: Olof Johansson <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/i2c/busses/i2c-cros-ec-tunnel.c

···
 	const u16 bus_num = bus->remote_bus;
 	int request_len;
 	int response_len;
+	int alloc_size;
 	int result;
-	struct cros_ec_command msg = { };
+	struct cros_ec_command *msg;
 
 	request_len = ec_i2c_count_message(i2c_msgs, num);
 	if (request_len < 0) {
···
 		return response_len;
 	}
 
-	result = ec_i2c_construct_message(msg.outdata, i2c_msgs, num, bus_num);
-	if (result)
-		return result;
+	alloc_size = max(request_len, response_len);
+	msg = kmalloc(sizeof(*msg) + alloc_size, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
 
-	msg.version = 0;
-	msg.command = EC_CMD_I2C_PASSTHRU;
-	msg.outsize = request_len;
-	msg.insize = response_len;
+	result = ec_i2c_construct_message(msg->data, i2c_msgs, num, bus_num);
+	if (result) {
+		dev_err(dev, "Error constructing EC i2c message %d\n", result);
+		goto exit;
+	}
 
-	result = cros_ec_cmd_xfer(bus->ec, &msg);
-	if (result < 0)
-		return result;
+	msg->version = 0;
+	msg->command = EC_CMD_I2C_PASSTHRU;
+	msg->outsize = request_len;
+	msg->insize = response_len;
 
-	result = ec_i2c_parse_response(msg.indata, i2c_msgs, &num);
-	if (result < 0)
-		return result;
+	result = cros_ec_cmd_xfer(bus->ec, msg);
+	if (result < 0) {
+		dev_err(dev, "Error transferring EC i2c message %d\n", result);
+		goto exit;
+	}
+
+	result = ec_i2c_parse_response(msg->data, i2c_msgs, &num);
+	if (result < 0) {
+		dev_err(dev, "Error parsing EC i2c message %d\n", result);
+		goto exit;
+	}
 
 	/* Indicate success by saying how many messages were sent */
-	return num;
+	result = num;
+exit:
+	kfree(msg);
+	return result;
 }
 
 static u32 ec_i2c_functionality(struct i2c_adapter *adap)

drivers/input/keyboard/cros_ec_keyb.c

···
 
 static int cros_ec_keyb_get_state(struct cros_ec_keyb *ckdev, uint8_t *kb_state)
 {
-	int ret;
-	struct cros_ec_command msg = {
-		.command = EC_CMD_MKBP_STATE,
-		.insize = ckdev->cols,
-	};
+	int ret = 0;
+	struct cros_ec_command *msg;
 
-	ret = cros_ec_cmd_xfer(ckdev->ec, &msg);
-	if (ret < 0)
-		return ret;
+	msg = kmalloc(sizeof(*msg) + ckdev->cols, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
 
-	memcpy(kb_state, msg.indata, ckdev->cols);
+	msg->version = 0;
+	msg->command = EC_CMD_MKBP_STATE;
+	msg->insize = ckdev->cols;
+	msg->outsize = 0;
 
-	return 0;
+	ret = cros_ec_cmd_xfer(ckdev->ec, msg);
+	if (ret < 0) {
+		dev_err(ckdev->dev, "Error transferring EC message %d\n", ret);
+		goto exit;
+	}
+
+	memcpy(kb_state, msg->data, ckdev->cols);
+exit:
+	kfree(msg);
+	return ret;
 }
 
 static irqreturn_t cros_ec_keyb_irq(int irq, void *data)

drivers/mfd/cros_ec.c

···
 	out[2] = msg->outsize;
 	csum = out[0] + out[1] + out[2];
 	for (i = 0; i < msg->outsize; i++)
-		csum += out[EC_MSG_TX_HEADER_BYTES + i] = msg->outdata[i];
+		csum += out[EC_MSG_TX_HEADER_BYTES + i] = msg->data[i];
 	out[EC_MSG_TX_HEADER_BYTES + msg->outsize] = (uint8_t)(csum & 0xff);
 
 	return EC_MSG_TX_PROTO_BYTES + msg->outsize;
···
 	ret = ec_dev->cmd_xfer(ec_dev, msg);
 	if (msg->result == EC_RES_IN_PROGRESS) {
 		int i;
-		struct cros_ec_command status_msg = { };
+		struct cros_ec_command *status_msg;
 		struct ec_response_get_comms_status *status;
 
-		status_msg.command = EC_CMD_GET_COMMS_STATUS;
-		status_msg.insize = sizeof(*status);
+		status_msg = kmalloc(sizeof(*status_msg) + sizeof(*status),
+				     GFP_KERNEL);
+		if (!status_msg) {
+			ret = -ENOMEM;
+			goto exit;
+		}
+
+		status_msg->version = 0;
+		status_msg->command = EC_CMD_GET_COMMS_STATUS;
+		status_msg->insize = sizeof(*status);
+		status_msg->outsize = 0;
 
 		/*
 		 * Query the EC's status until it's no longer busy or
···
 		for (i = 0; i < EC_COMMAND_RETRIES; i++) {
 			usleep_range(10000, 11000);
 
-			ret = ec_dev->cmd_xfer(ec_dev, &status_msg);
+			ret = ec_dev->cmd_xfer(ec_dev, status_msg);
 			if (ret < 0)
 				break;
 
-			msg->result = status_msg.result;
-			if (status_msg.result != EC_RES_SUCCESS)
+			msg->result = status_msg->result;
+			if (status_msg->result != EC_RES_SUCCESS)
 				break;
 
 			status = (struct ec_response_get_comms_status *)
-				 status_msg.indata;
+				 status_msg->data;
 			if (!(status->flags & EC_COMMS_STATUS_PROCESSING))
 				break;
 		}
+
+		kfree(status_msg);
 	}
+exit:
 	mutex_unlock(&ec_dev->lock);
 
 	return ret;

drivers/mfd/cros_ec_i2c.c

···
 	/* copy message payload and compute checksum */
 	sum = out_buf[0] + out_buf[1] + out_buf[2];
 	for (i = 0; i < msg->outsize; i++) {
-		out_buf[3 + i] = msg->outdata[i];
+		out_buf[3 + i] = msg->data[i];
 		sum += out_buf[3 + i];
 	}
 	out_buf[3 + msg->outsize] = sum;
···
 	/* copy response packet payload and compute checksum */
 	sum = in_buf[0] + in_buf[1];
 	for (i = 0; i < len; i++) {
-		msg->indata[i] = in_buf[2 + i];
+		msg->data[i] = in_buf[2 + i];
 		sum += in_buf[2 + i];
 	}
 	dev_dbg(ec_dev->dev, "packet: %*ph, sum = %02x\n",

drivers/mfd/cros_ec_spi.c

···
 	for (i = 0; i < len; i++) {
 		sum += ptr[i + 2];
 		if (ec_msg->insize)
-			ec_msg->indata[i] = ptr[i + 2];
+			ec_msg->data[i] = ptr[i + 2];
 	}
 	sum &= 0xff;
 

drivers/platform/chrome/cros_ec_dev.c

···
 #include <linux/fs.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
+#include <linux/slab.h>
 #include <linux/uaccess.h>
 
 #include "cros_ec_dev.h"
···
 	static const char * const current_image_name[] = {
 		"unknown", "read-only", "read-write", "invalid",
 	};
-	struct cros_ec_command msg = {
-		.version = 0,
-		.command = EC_CMD_GET_VERSION,
-		.outdata = { 0 },
-		.outsize = 0,
-		.indata = { 0 },
-		.insize = sizeof(*resp),
-	};
+	struct cros_ec_command *msg;
 	int ret;
 
-	ret = cros_ec_cmd_xfer(ec, &msg);
-	if (ret < 0)
-		return ret;
+	msg = kmalloc(sizeof(*msg) + sizeof(*resp), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
 
-	if (msg.result != EC_RES_SUCCESS) {
+	msg->version = 0;
+	msg->command = EC_CMD_GET_VERSION;
+	msg->insize = sizeof(*resp);
+	msg->outsize = 0;
+
+	ret = cros_ec_cmd_xfer(ec, msg);
+	if (ret < 0)
+		goto exit;
+
+	if (msg->result != EC_RES_SUCCESS) {
 		snprintf(str, maxlen,
 			 "%s\nUnknown EC version: EC returned %d\n",
-			 CROS_EC_DEV_VERSION, msg.result);
-		return 0;
+			 CROS_EC_DEV_VERSION, msg->result);
+		ret = -EINVAL;
+		goto exit;
 	}
 
-	resp = (struct ec_response_get_version *)msg.indata;
+	resp = (struct ec_response_get_version *)msg->data;
 	if (resp->current_image >= ARRAY_SIZE(current_image_name))
 		resp->current_image = 3; /* invalid */
 
···
 		 resp->version_string_ro, resp->version_string_rw,
 		 current_image_name[resp->current_image]);
 
-	return 0;
+	ret = 0;
+exit:
+	kfree(msg);
+	return ret;
 }
 
 /* Device file ops */
···
 static long ec_device_ioctl_xcmd(struct cros_ec_device *ec, void __user *arg)
 {
 	long ret;
-	struct cros_ec_command s_cmd = { };
+	struct cros_ec_command u_cmd;
+	struct cros_ec_command *s_cmd;
 
-	if (copy_from_user(&s_cmd, arg, sizeof(s_cmd)))
+	if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
 		return -EFAULT;
 
-	ret = cros_ec_cmd_xfer(ec, &s_cmd);
+	s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
+			GFP_KERNEL);
+	if (!s_cmd)
+		return -ENOMEM;
+
+	if (copy_from_user(s_cmd, arg, sizeof(*s_cmd) + u_cmd.outsize)) {
+		ret = -EFAULT;
+		goto exit;
+	}
+
+	ret = cros_ec_cmd_xfer(ec, s_cmd);
 	/* Only copy data to userland if data was received. */
 	if (ret < 0)
-		return ret;
+		goto exit;
 
-	if (copy_to_user(arg, &s_cmd, sizeof(s_cmd)))
-		return -EFAULT;
-
-	return 0;
+	if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + u_cmd.insize))
+		ret = -EFAULT;
+exit:
+	kfree(s_cmd);
+	return ret;
 }
 
 static long ec_device_ioctl_readmem(struct cros_ec_device *ec, void __user *arg)

drivers/platform/chrome/cros_ec_lightbar.c

···
 #include <linux/sched.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
+#include <linux/slab.h>
 
 #include "cros_ec_dev.h"
 
···
 	return ret;
 }
 
-#define INIT_MSG(P, R) { \
-		.command = EC_CMD_LIGHTBAR_CMD, \
-		.outsize = sizeof(*P), \
-		.insize = sizeof(*R), \
-	}
+static struct cros_ec_command *alloc_lightbar_cmd_msg(void)
+{
+	struct cros_ec_command *msg;
+	int len;
+
+	len = max(sizeof(struct ec_params_lightbar),
+		  sizeof(struct ec_response_lightbar));
+
+	msg = kmalloc(sizeof(*msg) + len, GFP_KERNEL);
+	if (!msg)
+		return NULL;
+
+	msg->version = 0;
+	msg->command = EC_CMD_LIGHTBAR_CMD;
+	msg->outsize = sizeof(struct ec_params_lightbar);
+	msg->insize = sizeof(struct ec_response_lightbar);
+
+	return msg;
+}
 
 static int get_lightbar_version(struct cros_ec_device *ec,
 				uint32_t *ver_ptr, uint32_t *flg_ptr)
 {
 	struct ec_params_lightbar *param;
 	struct ec_response_lightbar *resp;
-	struct cros_ec_command msg = INIT_MSG(param, resp);
+	struct cros_ec_command *msg;
 	int ret;
 
-	param = (struct ec_params_lightbar *)msg.outdata;
-	param->cmd = LIGHTBAR_CMD_VERSION;
-	ret = cros_ec_cmd_xfer(ec, &msg);
-	if (ret < 0)
+	msg = alloc_lightbar_cmd_msg();
+	if (!msg)
 		return 0;
 
-	switch (msg.result) {
+	param = (struct ec_params_lightbar *)msg->data;
+	param->cmd = LIGHTBAR_CMD_VERSION;
+	ret = cros_ec_cmd_xfer(ec, msg);
+	if (ret < 0) {
+		ret = 0;
+		goto exit;
+	}
+
+	switch (msg->result) {
 	case EC_RES_INVALID_PARAM:
 		/* Pixel had no version command. */
 		if (ver_ptr)
 			*ver_ptr = 0;
 		if (flg_ptr)
 			*flg_ptr = 0;
-		return 1;
+		ret = 1;
+		goto exit;
 
 	case EC_RES_SUCCESS:
-		resp = (struct ec_response_lightbar *)msg.indata;
+		resp = (struct ec_response_lightbar *)msg->data;
 
 		/* Future devices w/lightbars should implement this command */
 		if (ver_ptr)
 			*ver_ptr = resp->version.num;
 		if (flg_ptr)
 			*flg_ptr = resp->version.flags;
-		return 1;
+		ret = 1;
+		goto exit;
 	}
 
 	/* Anything else (ie, EC_RES_INVALID_COMMAND) - no lightbar */
-	return 0;
+	ret = 0;
+exit:
+	kfree(msg);
+	return ret;
 }
 
 static ssize_t version_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
-	uint32_t version, flags;
+	uint32_t version = 0, flags = 0;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
 	int ret;
 
···
 				const char *buf, size_t count)
 {
 	struct ec_params_lightbar *param;
-	struct ec_response_lightbar *resp;
-	struct cros_ec_command msg = INIT_MSG(param, resp);
+	struct cros_ec_command *msg;
 	int ret;
 	unsigned int val;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
···
 	if (kstrtouint(buf, 0, &val))
 		return -EINVAL;
 
-	param = (struct ec_params_lightbar *)msg.outdata;
+	msg = alloc_lightbar_cmd_msg();
+	if (!msg)
+		return -ENOMEM;
+
+	param = (struct ec_params_lightbar *)msg->data;
 	param->cmd = LIGHTBAR_CMD_BRIGHTNESS;
 	param->brightness.num = val;
 	ret = lb_throttle();
 	if (ret)
-		return ret;
+		goto exit;
 
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
-		return ret;
+		goto exit;
 
-	if (msg.result != EC_RES_SUCCESS)
-		return -EINVAL;
+	if (msg->result != EC_RES_SUCCESS) {
+		ret = -EINVAL;
+		goto exit;
+	}
 
-	return count;
+	ret = count;
+exit:
+	kfree(msg);
+	return ret;
 }
 
 
···
 			     const char *buf, size_t count)
 {
 	struct ec_params_lightbar *param;
-	struct ec_response_lightbar *resp;
-	struct cros_ec_command msg = INIT_MSG(param, resp);
+	struct cros_ec_command *msg;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
 	unsigned int val[4];
 	int ret, i = 0, j = 0, ok = 0;
+
+	msg = alloc_lightbar_cmd_msg();
+	if (!msg)
+		return -ENOMEM;
 
 	do {
 		/* Skip any whitespace */
···
 			return -EINVAL;
 
 		if (i == 4) {
-			param = (struct ec_params_lightbar *)msg.outdata;
+			param = (struct ec_params_lightbar *)msg->data;
 			param->cmd = LIGHTBAR_CMD_RGB;
 			param->rgb.led = val[0];
 			param->rgb.red = val[1];
···
 					return ret;
 			}
 
-			ret = cros_ec_cmd_xfer(ec, &msg);
+			ret = cros_ec_cmd_xfer(ec, msg);
 			if (ret < 0)
-				return ret;
+				goto exit;
 
-			if (msg.result != EC_RES_SUCCESS)
-				return -EINVAL;
+			if (msg->result != EC_RES_SUCCESS) {
+				ret = -EINVAL;
+				goto exit;
+			}
 
 			i = 0;
 			ok = 1;
···
 
 	} while (*buf);
 
+exit:
+	kfree(msg);
 	return (ok && i == 0) ? count : -EINVAL;
 }
 
···
 {
 	struct ec_params_lightbar *param;
 	struct ec_response_lightbar *resp;
-	struct cros_ec_command msg = INIT_MSG(param, resp);
+	struct cros_ec_command *msg;
 	int ret;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
 
-	param = (struct ec_params_lightbar *)msg.outdata;
+	msg = alloc_lightbar_cmd_msg();
+	if (!msg)
+		return -ENOMEM;
+
+	param = (struct ec_params_lightbar *)msg->data;
 	param->cmd = LIGHTBAR_CMD_GET_SEQ;
 	ret = lb_throttle();
 	if (ret)
-		return ret;
+		goto exit;
 
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
-		return ret;
+		goto exit;
 
-	if (msg.result != EC_RES_SUCCESS)
-		return scnprintf(buf, PAGE_SIZE,
-				 "ERROR: EC returned %d\n", msg.result);
+	if (msg->result != EC_RES_SUCCESS) {
+		ret = scnprintf(buf, PAGE_SIZE,
+				"ERROR: EC returned %d\n", msg->result);
+		goto exit;
+	}
 
-	resp = (struct ec_response_lightbar *)msg.indata;
+	resp = (struct ec_response_lightbar *)msg->data;
 	if (resp->get_seq.num >= ARRAY_SIZE(seqname))
-		return scnprintf(buf, PAGE_SIZE, "%d\n", resp->get_seq.num);
+		ret = scnprintf(buf, PAGE_SIZE, "%d\n", resp->get_seq.num);
 	else
-		return scnprintf(buf, PAGE_SIZE, "%s\n",
-				 seqname[resp->get_seq.num]);
+		ret = scnprintf(buf, PAGE_SIZE, "%s\n",
+				seqname[resp->get_seq.num]);
+
+exit:
+	kfree(msg);
+	return ret;
 }
 
 static ssize_t sequence_store(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
 	struct ec_params_lightbar *param;
-	struct ec_response_lightbar *resp;
-	struct cros_ec_command msg = INIT_MSG(param, resp);
+	struct cros_ec_command *msg;
 	unsigned int num;
 	int ret, len;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
+
+	msg = alloc_lightbar_cmd_msg();
+	if (!msg)
+		return -ENOMEM;
 
 	for (len = 0; len < count; len++)
 		if (!isalnum(buf[len]))
···
 			return ret;
 	}
 
-	param = (struct ec_params_lightbar *)msg.outdata;
+	param = (struct ec_params_lightbar *)msg->data;
 	param->cmd = LIGHTBAR_CMD_SEQ;
 	param->seq.num = num;
 	ret = lb_throttle();
 	if (ret)
 		return ret;
 
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
 		return ret;
 
-	if (msg.result != EC_RES_SUCCESS)
+	if (msg->result != EC_RES_SUCCESS)
 		return -EINVAL;
 
 	return count;

drivers/platform/chrome/cros_ec_lpc.c

···
 
 	/* Copy data and update checksum */
 	for (i = 0; i < msg->outsize; i++) {
-		outb(msg->outdata[i], EC_LPC_ADDR_HOST_PARAM + i);
-		csum += msg->outdata[i];
+		outb(msg->data[i], EC_LPC_ADDR_HOST_PARAM + i);
+		csum += msg->data[i];
 	}
 
 	/* Finalize checksum and write args */
···
 
 	/* Read response and update checksum */
 	for (i = 0; i < args.data_size; i++) {
-		msg->indata[i] = inb(EC_LPC_ADDR_HOST_PARAM + i);
-		csum += msg->indata[i];
+		msg->data[i] = inb(EC_LPC_ADDR_HOST_PARAM + i);
+		csum += msg->data[i];
 	}
 
 	/* Verify checksum */

drivers/platform/chrome/cros_ec_sysfs.c

···
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/printk.h>
+#include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
···
 		{"hibernate",    EC_REBOOT_HIBERNATE, 0},
 		{"at-shutdown",  -1, EC_REBOOT_FLAG_ON_AP_SHUTDOWN},
 	};
-	struct cros_ec_command msg = { 0 };
-	struct ec_params_reboot_ec *param =
-		(struct ec_params_reboot_ec *)msg.outdata;
+	struct cros_ec_command *msg;
+	struct ec_params_reboot_ec *param;
 	int got_cmd = 0, offset = 0;
 	int i;
 	int ret;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
+
+	msg = kmalloc(sizeof(*msg) + sizeof(*param), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	param = (struct ec_params_reboot_ec *)msg->data;
 
 	param->flags = 0;
 	while (1) {
···
 			offset++;
 	}
 
-	if (!got_cmd)
-		return -EINVAL;
-
-	msg.command = EC_CMD_REBOOT_EC;
-	msg.outsize = sizeof(param);
-	ret = cros_ec_cmd_xfer(ec, &msg);
-	if (ret < 0)
-		return ret;
-	if (msg.result != EC_RES_SUCCESS) {
-		dev_dbg(ec->dev, "EC result %d\n", msg.result);
-		return -EINVAL;
+	if (!got_cmd) {
+		count = -EINVAL;
+		goto exit;
 	}
 
+	msg->version = 0;
+	msg->command = EC_CMD_REBOOT_EC;
+	msg->outsize = sizeof(*param);
+	msg->insize = 0;
+	ret = cros_ec_cmd_xfer(ec, msg);
+	if (ret < 0) {
+		count = ret;
+		goto exit;
+	}
+	if (msg->result != EC_RES_SUCCESS) {
+		dev_dbg(ec->dev, "EC result %d\n", msg->result);
+		count = -EINVAL;
+	}
+exit:
+	kfree(msg);
 	return count;
 }
 
···
 	struct ec_response_get_version *r_ver;
 	struct ec_response_get_chip_info *r_chip;
 	struct ec_response_board_version *r_board;
-	struct cros_ec_command msg = { 0 };
+	struct cros_ec_command *msg;
 	int ret;
 	int count = 0;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
 
-	/* Get versions. RW may change. */
-	msg.command = EC_CMD_GET_VERSION;
-	msg.insize = sizeof(*r_ver);
-	ret = cros_ec_cmd_xfer(ec, &msg);
-	if (ret < 0)
-		return ret;
-	if (msg.result != EC_RES_SUCCESS)
-		return scnprintf(buf, PAGE_SIZE,
-				 "ERROR: EC returned %d\n", msg.result);
+	msg = kmalloc(sizeof(*msg) + EC_HOST_PARAM_SIZE, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
 
-	r_ver = (struct ec_response_get_version *)msg.indata;
+	/* Get versions. RW may change. */
+	msg->version = 0;
+	msg->command = EC_CMD_GET_VERSION;
+	msg->insize = sizeof(*r_ver);
+	msg->outsize = 0;
+	ret = cros_ec_cmd_xfer(ec, msg);
+	if (ret < 0) {
+		count = ret;
+		goto exit;
+	}
+	if (msg->result != EC_RES_SUCCESS) {
+		count = scnprintf(buf, PAGE_SIZE,
+				  "ERROR: EC returned %d\n", msg->result);
+		goto exit;
+	}
+
+	r_ver = (struct ec_response_get_version *)msg->data;
 	/* Strings should be null-terminated, but let's be sure. */
 	r_ver->version_string_ro[sizeof(r_ver->version_string_ro) - 1] = '\0';
 	r_ver->version_string_rw[sizeof(r_ver->version_string_rw) - 1] = '\0';
···
 			    image_names[r_ver->current_image] : "?"));
 
 	/* Get build info. */
-	msg.command = EC_CMD_GET_BUILD_INFO;
-	msg.insize = sizeof(msg.indata);
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	msg->command = EC_CMD_GET_BUILD_INFO;
+	msg->insize = EC_HOST_PARAM_SIZE;
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
 				   "Build info:    XFER ERROR %d\n", ret);
-	else if (msg.result != EC_RES_SUCCESS)
+	else if (msg->result != EC_RES_SUCCESS)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
-				   "Build info:    EC error %d\n", msg.result);
+				   "Build info:    EC error %d\n", msg->result);
 	else {
-		msg.indata[sizeof(msg.indata) - 1] = '\0';
+		msg->data[sizeof(msg->data) - 1] = '\0';
 		count += scnprintf(buf + count, PAGE_SIZE - count,
-				   "Build info:    %s\n", msg.indata);
+				   "Build info:    %s\n", msg->data);
 	}
 
 	/* Get chip info. */
-	msg.command = EC_CMD_GET_CHIP_INFO;
-	msg.insize = sizeof(*r_chip);
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	msg->command = EC_CMD_GET_CHIP_INFO;
+	msg->insize = sizeof(*r_chip);
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
 				   "Chip info:     XFER ERROR %d\n", ret);
-	else if (msg.result != EC_RES_SUCCESS)
+	else if (msg->result != EC_RES_SUCCESS)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
-				   "Chip info:     EC error %d\n", msg.result);
+				   "Chip info:     EC error %d\n", msg->result);
 	else {
-		r_chip = (struct ec_response_get_chip_info *)msg.indata;
+		r_chip = (struct ec_response_get_chip_info *)msg->data;
 
 		r_chip->vendor[sizeof(r_chip->vendor) - 1] = '\0';
 		r_chip->name[sizeof(r_chip->name) - 1] = '\0';
···
 	}
 
 	/* Get board version */
-	msg.command = EC_CMD_GET_BOARD_VERSION;
-	msg.insize = sizeof(*r_board);
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	msg->command = EC_CMD_GET_BOARD_VERSION;
+	msg->insize = sizeof(*r_board);
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
 				   "Board version: XFER ERROR %d\n", ret);
-	else if (msg.result != EC_RES_SUCCESS)
+	else if (msg->result != EC_RES_SUCCESS)
 		count += scnprintf(buf + count, PAGE_SIZE - count,
-				   "Board version: EC error %d\n", msg.result);
+				   "Board version: EC error %d\n", msg->result);
 	else {
-		r_board = (struct ec_response_board_version *)msg.indata;
+		r_board = (struct ec_response_board_version *)msg->data;
 
 		count += scnprintf(buf + count, PAGE_SIZE - count,
 				   "Board version: %d\n",
 				   r_board->board_version);
 	}
 
+exit:
+	kfree(msg);
 	return count;
 }
 
···
 				 struct device_attribute *attr, char *buf)
 {
 	struct ec_response_flash_info *resp;
-	struct cros_ec_command msg = { 0 };
+	struct cros_ec_command *msg;
 	int ret;
 	struct cros_ec_device *ec = dev_get_drvdata(dev);
 
+	msg = kmalloc(sizeof(*msg) + sizeof(*resp), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
 	/* The flash info shouldn't ever change, but ask each time anyway. */
-	msg.command = EC_CMD_FLASH_INFO;
-	msg.insize = sizeof(*resp);
-	ret = cros_ec_cmd_xfer(ec, &msg);
+	msg->version = 0;
+	msg->command = EC_CMD_FLASH_INFO;
+	msg->insize = sizeof(*resp);
+	msg->outsize = 0;
+	ret = cros_ec_cmd_xfer(ec, msg);
 	if (ret < 0)
-		return ret;
-	if (msg.result != EC_RES_SUCCESS)
-		return scnprintf(buf, PAGE_SIZE,
-				 "ERROR: EC returned %d\n", msg.result);
+		goto exit;
+	if (msg->result != EC_RES_SUCCESS) {
+		ret = scnprintf(buf, PAGE_SIZE,
+				"ERROR: EC returned %d\n", msg->result);
+		goto exit;
+	}
 
-	resp = (struct ec_response_flash_info *)msg.indata;
+	resp = (struct ec_response_flash_info *)msg->data;
 
-	return scnprintf(buf, PAGE_SIZE,
-			 "FlashSize %d\nWriteSize %d\n"
-			 "EraseSize %d\nProtectSize %d\n",
-			 resp->flash_size, resp->write_block_size,
-			 resp->erase_block_size, resp->protect_block_size);
+	ret = scnprintf(buf, PAGE_SIZE,
+			"FlashSize %d\nWriteSize %d\n"
+			"EraseSize %d\nProtectSize %d\n",
+			resp->flash_size, resp->write_block_size,
+			resp->erase_block_size, resp->protect_block_size);
+exit:
+	kfree(msg);
+	return ret;
 }
 
 /* Module initialization */

include/linux/mfd/cros_ec.h

···
  * @outsize: Outgoing length in bytes
  * @insize: Max number of bytes to accept from EC
  * @result: EC's response to the command (separate from communication failure)
- * @outdata: Outgoing data to EC
- * @indata: Where to put the incoming data from EC
+ * @data: Where to put the incoming data from EC and outgoing data to EC
  */
 struct cros_ec_command {
 	uint32_t version;
···
 	uint32_t outsize;
 	uint32_t insize;
 	uint32_t result;
-	uint8_t outdata[EC_PROTO2_MAX_PARAM_SIZE];
-	uint8_t indata[EC_PROTO2_MAX_PARAM_SIZE];
+	uint8_t data[0];
 };
 
 /**