Messages in this thread Patch in this message | | | Date | Wed, 18 Nov 2009 11:08:11 +0100 (CET) | From | Jiri Kosina <> | Subject | [PATCH] Do not read IIR in serial8250_start_tx when UART_BUG_TXEN |
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The patch below has been lost several times (the last submission happened probably on [1]). I am currently aware of a real hardware which triggers this problem quite reliably, so we should rather have that really fixed.
[1] http://lkml.org/lkml/2009/3/12/379
From: Ian Jackson <ian.jackson@eu.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@eu.citrix.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Jiri Kosina <jkosina@suse.cz>
--- 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 737b4c9..807042b 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); } }
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