linux-kernel - [42/90] Serial: Do not read IIR in serial8250_start_tx when UART_BUG

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Date:	Wed, 16 Dec 2009 17:14:53 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Ian Jackson <ian.jackson@...citrix.com>,
	Alan Cox <alan@...ux.intel.com>
Subject: [42/90] Serial: Do not read IIR in serial8250_start_tx when UART_BUG_TXEN

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------

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

commit 68cb4f8e246bbbc649980be0628cae9265870a91 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/serial/8250.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1337,14 +1337,12 @@ static void serial8250_start_tx(struct u
 		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);
 		}
 	}


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