Add xscom_ok() and lpc_ok() to check XSCOM and LPC usability

his primarily checks whether the caller already holds the corresponding
locks to avoid re-entrancy in some of the deep error path such as when
XSCOM itself triggers an error log. It will be extended in the case of
LPC to also handle known HW error states.

We use them to avoid queuing/polling in the BT driver and to discard
characters in the UART driver.

Note: This will not normally involve a loss of log to the UART as the
UART driver is also protected by the console suspend mechanism. So
this is a safety mechanism only.

This fixes issues where the generation of error logs inside the LPC or
XSCOM drivers could cause a re-entrancy (via the BT interface)
causing deadlocks. Now, the error logs IPMI messages will be queued up
and delivered later on the next poll handler.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/hw/lpc-uart.c b/hw/lpc-uart.c
index 2e6114ac..7c3190e3 100644
--- a/hw/lpc-uart.c
+++ b/hw/lpc-uart.c
@@ -135,6 +135,10 @@ static size_t uart_con_write(const char *buf, size_t len)
 {
 	size_t written = 0;
 
+	/* If LPC bus is bad, we just swallow data */
+	if (!lpc_ok())
+		return written;
+
 	lock(&uart_lock);
 	while(written < len) {
 		if (tx_room == 0) {