linux-kernel - [PATCH 23/58] Serial: Do not read IIR in serial8250_start_tx when UART_BUG

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Message-Id: <1260574122-10676-23-git-send-email-gregkh@suse.de>
Date:	Fri, 11 Dec 2009 15:28:07 -0800
From:	Greg Kroah-Hartman <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	Ian Jackson <ian.jackson@...citrix.com>,
	Alan Cox <alan@...ux.intel.com>, stable <stable@...nel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 23/58] Serial: Do not read IIR in serial8250_start_tx when UART_BUG_TXEN

From: Ian Jackson <ian.jackson@...citrix.com>

Do not read IIR in serial8250_start_tx when UART_BUG_TXEN

Reading the IIR clears some oustanding interrupts so it is not safe.
Instead, simply transmit immediately if the buffer is empty without
regard to IIR.

Signed-off-by: Ian Jackson <ian.jackson@...citrix.com>
Reviewed-by: Markus Armbruster <armbru@...hat.com>
Reviewed-by: Jiri Kosina <jkosina@...e.cz>
Cc: Alan Cox <alan@...ux.intel.com>
Cc: stable <stable@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 drivers/serial/8250.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index b75e63e..c3e37c8 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1339,14 +1339,12 @@ static void serial8250_start_tx(struct uart_port *port)
 		serial_out(up, UART_IER, up->ier);
 
 		if (up->bugs & UART_BUG_TXEN) {
-			unsigned char lsr, iir;
+			unsigned char lsr;
 			lsr = serial_in(up, UART_LSR);
 			up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
-			iir = serial_in(up, UART_IIR) & 0x0f;
 			if ((up->port.type == PORT_RM9000) ?
-				(lsr & UART_LSR_THRE &&
-				(iir == UART_IIR_NO_INT || iir == UART_IIR_THRI)) :
-				(lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT))
+				(lsr & UART_LSR_THRE) :
+				(lsr & UART_LSR_TEMT))
 				transmit_chars(up);
 		}
 	}
-- 
1.6.5.5

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