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 <gwendal@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

1 files changed, 19 insertions, 10 deletions

diff --git a/drivers/input/keyboard/cros_ec_keyb.c b/drivers/input/keyboard/cros_ec_keyb.c
index b50c5b8b8a4d..974154a74505 100644
--- a/drivers/input/keyboard/cros_ec_keyb.c
+++ b/drivers/input/keyboard/cros_ec_keyb.c
@@ -148,19 +148,28 @@ static void cros_ec_keyb_process(struct cros_ec_keyb *ckdev,
 
 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)