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SubjectRe: [PATCH v2] mfd: cros_ec: check for NULL transfer function
Reviewed-by: Jett Rink <jettrink@chromium.org>

On Wed, Apr 3, 2019 at 4:40 PM <egranata@chromium.org> wrote:
>
> From: Enrico Granata <egranata@chromium.org>
>
> As new transfer mechanisms are added to the EC codebase, they may
> not support v2 of the EC protocol.
>
> If the v3 initial handshake transfer fails, the kernel will try
> and call cmd_xfer as a fallback. If v2 is not supported, cmd_xfer
> will be NULL, and the code will end up causing a kernel panic.
>
> Add a check for NULL before calling the transfer function, along
> with a helpful comment explaining how one might end up in this
> situation.
>
> Signed-off-by: Enrico Granata <egranata@chromium.org>
> ---
> drivers/platform/chrome/cros_ec_proto.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
> index 97a068dff192d..55691656a3c27 100644
> --- a/drivers/platform/chrome/cros_ec_proto.c
> +++ b/drivers/platform/chrome/cros_ec_proto.c
> @@ -56,6 +56,16 @@ static int send_command(struct cros_ec_device *ec_dev,
> else
> xfer_fxn = ec_dev->cmd_xfer;
>
> + if (xfer_fxn == NULL) {
> + /* This error can happen if a communication error happened and
> + * the EC is trying to use protocol v2, on an underlying
> + * communication mechanism that does not support v2.
> + */
> + dev_err_once(ec_dev->dev,
> + "missing EC transfer API, cannot send command\n");
> + return -EIO;
> + }
> +
> ret = (*xfer_fxn)(ec_dev, msg);
> if (msg->result == EC_RES_IN_PROGRESS) {
> int i;
> --
> 2.21.0.392.gf8f6787159e-goog
>

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