Fix for dropped xmit data on 16654 UART.
serial.c 2.4.20-rc1
This trivial patch limits execution of the Elan work-around code to
UARTs detected as type 8250, 16450, 16550 and 16550A. During transmit,
the Exar 16C654 UART frequently has leftover THRI status visible in
its IIR register when the THRE status is not present in the LSR
register and a transmit interrupt is not pending. This interacts with
the Elan LSR timing work-around to cause serial driver to write more
data to a 16C654 UART before the UART is ready to take it.
----------------------------------------------------------------
Ed Vance edv (at) macrolink (dot) com
Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807
----------------------------------------------------------------
diff -urN -X dontdiff.txt linux-2.4.20-rc1/drivers/char/serial.c
linux-654fix/drivers/char/serial.c
--- linux-2.4.20-rc1/drivers/char/serial.c Mon Oct 28 12:19:17 2002
+++ linux-654fix/drivers/char/serial.c Wed Oct 30 10:12:00 2002
@@ -792,6 +792,23 @@
}
}
+/*
+ * Returns != 0 (true) if UART is ready for more transmit data.
+ * This function contains a work-around for a silicon bug in the UARTs
+ * of the AMD Elan microcontroller. The LSR THRE bit is set late and
+ * may be missed by the interrupt routine, so an IIR THRI status is also
+ * treated as an LSR THRE status. This causes xmit data loss on 16C654
+ * UARTs (and perhaps others) so the work-around is applied only to
+ * ports detected as generic UART types 8250, 16450, 16550 and 16550A.
+ */
+static _INLINE_ int uart_transmit_ready(struct async_struct *info,
+ int status, int iir)
+{
+ return (status & UART_LSR_THRE) ||
+ ((info->state->type <= PORT_16550A) &&
+ ((iir & UART_IIR_ID) == UART_IIR_THRI));
+}
+
#ifdef CONFIG_SERIAL_SHARE_IRQ
/*
* This is the serial driver's generic interrupt routine
@@ -842,9 +859,7 @@
if (status & UART_LSR_DR)
receive_chars(info, &status, regs);
check_modem_status(info);
- if ((status & UART_LSR_THRE) ||
- /* for buggy ELAN processors */
- ((iir & UART_IIR_ID) == UART_IIR_THRI))
+ if (uart_transmit_ready(info, status, iir))
transmit_chars(info, 0);
next:
@@ -909,9 +924,7 @@
if (status & UART_LSR_DR)
receive_chars(info, &status, regs);
check_modem_status(info);
- if ((status & UART_LSR_THRE) ||
- /* For buggy ELAN processors */
- ((iir & UART_IIR_ID) == UART_IIR_THRI))
+ if (uart_transmit_ready(info, status, iir))
transmit_chars(info, 0);
if (pass_counter++ > RS_ISR_PASS_LIMIT) {
#if SERIAL_DEBUG_INTR
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:55 EST