PowerNV: add buffer for OPAL console

Avoid the lock in vtophys() by providing a static direct-mapped
spinlock- protected output buffer to use when the console driver
cannot acquire locks for some reason. This allows the idle thread
to use printf() (e.g. the SMP startup messages) without crashing
the kernel.

Created by:            Nathan Whitehorn <nwhitehorn@freebsd.org>
Submitted by:          Wojciech Macek <wma@freebsd.org>
Sponsored by:          FreeBSD Foundation

1 files changed, 54 insertions, 10 deletions

diff --git a/sys/powerpc/powernv/opal_console.c b/sys/powerpc/powernv/opal_console.c
index 5d2046c685f2..ac39e71dbf2c 100644
--- a/sys/powerpc/powernv/opal_console.c
+++ b/sys/powerpc/powernv/opal_console.c
@@ -34,6 +34,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/types.h>
 #include <sys/conf.h>
 #include <sys/cons.h>
+#include <sys/proc.h>
 #include <sys/tty.h>
 
 #include <vm/vm.h>
@@ -72,6 +73,7 @@ struct uart_opal_softc {
 };
 
 static struct uart_opal_softc	*console_sc = NULL;
+
 #if defined(KDB)
 static int			alt_break_state;
 #endif
@@ -127,6 +129,48 @@ static struct ttydevsw uart_opal_tty_class = {
 	.tsw_outwakeup	= uart_opal_ttyoutwakeup,
 };
 
+static struct {
+	char tmpbuf[16];
+	uint64_t size;
+	struct mtx mtx;
+} escapehatch;
+
+static void
+uart_opal_real_map_outbuffer(uint64_t *bufferp, uint64_t *lenp)
+{
+
+	if (!mtx_initialized(&escapehatch.mtx))
+		mtx_init(&escapehatch.mtx, "uart_opal", NULL, MTX_SPIN | MTX_QUIET |
+		    MTX_NOWITNESS);
+
+	if (!pmap_bootstrapped)
+		return;
+
+	if (TD_IS_IDLETHREAD(curthread)) {
+		escapehatch.size = *(uint64_t *)(*lenp) =
+		    min(sizeof(escapehatch.tmpbuf), *(uint64_t *)(*lenp));
+		mtx_lock_spin(&escapehatch.mtx);
+		memcpy(escapehatch.tmpbuf, (void *)(*bufferp), *(uint64_t *)(*lenp));
+		*bufferp = (uint64_t)escapehatch.tmpbuf;
+		*lenp = (uint64_t)&escapehatch.size;
+	}
+
+	*bufferp = vtophys(*bufferp);
+	*lenp = vtophys(*lenp);
+}
+	
+static void
+uart_opal_real_unmap_outbuffer(uint64_t lenp, uint64_t *origlen)
+{
+
+	if (!pmap_bootstrapped || !TD_IS_IDLETHREAD(curthread))
+		return;
+
+	mtx_assert(&escapehatch.mtx, MA_OWNED);
+	*origlen = escapehatch.size;
+	mtx_unlock_spin(&escapehatch.mtx);
+}
+
 static int
 uart_opal_probe_node(struct uart_opal_softc *sc)
 {
@@ -231,6 +275,7 @@ uart_opal_attach(device_t dev)
 	    MTX_SPIN | MTX_QUIET | MTX_NOWITNESS);
 
 	if (console_sc != NULL && console_sc->vtermid == sc->vtermid) {
+		device_printf(dev, "console\n");
 		sc->outseqno = console_sc->outseqno;
 		console_sc = sc;
 		sprintf(uart_opal_consdev.cn_name, "ttyu%r", unit);
@@ -332,25 +377,20 @@ static int
 uart_opal_put(struct uart_opal_softc *sc, void *buffer, size_t bufsize)
 {
 	uint16_t seqno;
-	uint64_t len = bufsize;
+	uint64_t len;
 	char	cbuf[16];
 	int	err;
 	uint64_t olen = (uint64_t)&len;
 	uint64_t obuf = (uint64_t)cbuf;
 
-	if (pmap_bootstrapped)
-		olen = vtophys(&len);
-
 	if (sc->protocol == OPAL_RAW) {
-		if (pmap_bootstrapped)
-			obuf = vtophys(buffer);
-		else
-			obuf = (uint64_t)(buffer);
+		obuf = (uint64_t)buffer;
+		len = bufsize;
 
+		uart_opal_real_map_outbuffer(&obuf, &olen);
 		err = opal_call(OPAL_CONSOLE_WRITE, sc->vtermid, olen, obuf);
+		uart_opal_real_unmap_outbuffer(olen, &len);
 	} else {
-		if (pmap_bootstrapped)
-			obuf = vtophys(cbuf);
 		uart_lock(&sc->sc_mtx);
 		if (bufsize > 12)
 			bufsize = 12;
@@ -361,7 +401,11 @@ uart_opal_put(struct uart_opal_softc *sc, void *buffer, size_t bufsize)
 		cbuf[3] = seqno & 0xff;
 		memcpy(&cbuf[4], buffer, bufsize);
 		len = 4 + bufsize;
+
+		uart_opal_real_map_outbuffer(&obuf, &olen);
 		err = opal_call(OPAL_CONSOLE_WRITE, sc->vtermid, olen, obuf);
+		uart_opal_real_unmap_outbuffer(olen, &len);
+
 		uart_unlock(&sc->sc_mtx);
 
 		len -= 4;