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Commit 68cb4f8e authored by Ian Jackson's avatar Ian Jackson Committed by Greg Kroah-Hartman
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Serial: Do not read IIR in serial8250_start_tx when UART_BUG_TXEN 



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: default avatarIan Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: default avatarMarkus Armbruster <armbru@redhat.com>
Reviewed-by: default avatarJiri Kosina <jkosina@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 7e11a0fb

drivers/serial/8250.c

+3 −5
Original line number Diff line number Diff line
@@ -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);

		}

	}