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ns16550a: Buy back 16088 asy can overrun TX on interrupt race #57

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ns16550a: Buy back 16088 asy can overrun TX on interrupt race #57

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60 changes: 41 additions & 19 deletions usr/src/uts/armv8/io/ns16550a/ns16550a.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1969,18 +1969,17 @@ ns16550_baudok(struct ns16550com *ns16550)
uint_t
ns16550intr(caddr_t argns16550)
{
struct ns16550com *ns16550 = (struct ns16550com *)argns16550;
struct nsasyncline *nsasync;
struct ns16550com *ns16550 = (struct ns16550com *)argns16550;
struct nsasyncline *nsasync = ns16550->ns16550_priv;
int ret_status = DDI_INTR_UNCLAIMED;
uchar_t interrupt_id, lsr;

interrupt_id = ns16550_get_isr(ns16550);
nsasync = ns16550->ns16550_priv;
if ((nsasync == NULL) ||
!(nsasync->nsasync_flags & (NSASYNC_ISOPEN|NSASYNC_WOPEN))) {
if (interrupt_id & NOINTERRUPT)
const uint8_t intr_id = ns16550_get_isr(ns16550);

if (intr_id & NOINTERRUPT) {
return (DDI_INTR_UNCLAIMED);
else {
} else {
/*
* reset the device by:
* reading line status
Expand All @@ -2005,33 +2004,56 @@ ns16550intr(caddr_t argns16550)
* We will loop until the interrupt line is pulled low. ns16550
* interrupt is edge triggered.
*/
/* CSTYLED */
for (;; interrupt_id =
ns16550_get_isr(ns16550)) {
for (;;) {
const uint8_t intr_id = ns16550_get_isr(ns16550);

if (interrupt_id & NOINTERRUPT)
if (intr_id & NOINTERRUPT)
break;
ret_status = DDI_INTR_CLAIMED;

DEBUGCONT1(NS16550_DEBUG_INTR, "ns16550intr: interrupt_id = 0x%d\n",
interrupt_id);
lsr = ns16550_get_lsr(ns16550);
switch (interrupt_id) {
DEBUGCONT1(NS16550_DEBUG_INTR, "ns16550intr: intr_id = 0x%d\n",
intr_id);

const uint8_t lsr = ns16550_get_lsr(ns16550);

switch (intr_id) {
case TxRDY:
/*
* The transmit-ready interrupt implies an empty
* transmit-hold register (or FIFO). Check that it is
* present before attempting to transmit more data.
*/
if ((lsr & XHRE) == 0) {
/*
* Taking a TxRDY interrupt only to find XHRE
* absent would be a surprise, except for a
* racing ns16550putchar(), which ignores the
* excl_hi mutex when writing to the device.
*/
continue;
}

nsasync_txint(ns16550);

/*
* Unlike the other interrupts which fall through to
* attempting to fill the output register/FIFO, TxRDY
* has no need having just done so.
*/
continue;
case RxRDY:
case RSTATUS:
case FFTMOUT:
/* receiver interrupt or receiver errors */
nsasync_rxint(ns16550, lsr);
break;
case TxRDY:
/* transmit interrupt */
nsasync_txint(ns16550);
continue;
case MSTATUS:
/* modem status interrupt */
nsasync_msint(ns16550);
break;
}

/* Refill the output FIFO if it has gone empty */
if ((lsr & XHRE) && (nsasync->nsasync_flags & NSASYNC_BUSY) &&
(nsasync->nsasync_ocnt > 0))
nsasync_txint(ns16550);
Expand Down