[Skiboot] [PATCH v2 1/3] hw/bt: Fix bt_add_ipmi_msg_head() logic

[Andrew Jeffery]

On Fri, 22 Feb 2019, at 02:37, Vasant Hegde wrote:
> BT send logic always sends top of bt message list to BMC. Once BMC reads the
> message, it clears the interrupt and bt_idle() becomes true.
> 
> bt_add_ipmi_msg_head() adds message to top of the list. If bt message list
> is not empty then:
>   - if bt_idle() is true then we will endup sending message to BMC before
>     getting response from BMC for inflight message. Looks like on some
>     BMC implementation this results in message timeout.
>   - else we endup starting message timer without actually sending message
>     to BMC.. which is not correct.
> 
> This patch fixes above described issue by adding message to right place
> in the list.
> 
> Signed-off-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
> ---
> Stewart,
>   All I'm doing is list_pop/list_add. May be we can have new function
>   (list_add_after()>. Let me know whether you are ok with this patch
>    -OR- want me to add list_add_after()>
> 
> -Vasant
> 
>  hw/bt.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/bt.c b/hw/bt.c
> index 5a6bc3cde..a3561953b 100644
> --- a/hw/bt.c
> +++ b/hw/bt.c
> @@ -533,11 +533,20 @@ static void bt_add_msg(struct bt_msg *bt_msg)
>  
>  static int bt_add_ipmi_msg_head(struct ipmi_msg *ipmi_msg)
>  {
> +	struct bt_msg *tmp_bt_msg;
>  	struct bt_msg *bt_msg = container_of(ipmi_msg, struct bt_msg, ipmi_msg);
>  
>  	lock(&bt.lock);
>  	bt_add_msg(bt_msg);
> -	list_add(&bt.msgq, &bt_msg->link);
> +
> +	if (list_empty(&bt.msgq)) {
> +		list_add(&bt.msgq, &bt_msg->link);
> +	} else {
> +		/* Add message after top message */
> +		tmp_bt_msg = list_pop(&bt.msgq, struct bt_msg, link);
> +		list_add(&bt.msgq, &bt_msg->link);
> +		list_add(&bt.msgq, &tmp_bt_msg->link);

This looks a bit contorted. Is it worth having a separate pointer for the
in-flight message so we're not storing it at the head of the list?

> +	}
>  	bt_send_and_unlock();
>  
>  	return 0;
> -- 
> 2.14.3
> 
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