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authorDick Hollenbeck <dick@softplc.com>2009-12-09 12:31:34 -0800
committerGreg Kroah-Hartman <gregkh@suse.de>2010-04-01 15:55:53 -0700
commit354a8d03e60a13600346babc1a78ecce4075f917 (patch)
treef98b1a5f70a0aec2c87641d04b888aad39168af0
parent6590bda22d4fd456ddbf8e70077e247d3014c333 (diff)
downloadlwn-354a8d03e60a13600346babc1a78ecce4075f917.tar.gz
lwn-354a8d03e60a13600346babc1a78ecce4075f917.zip
serial: 8250: add serial transmitter fully empty test
commit bca476139d2ded86be146dae09b06e22548b67f3 upstream. When controlling an industrial radio modem it can be necessary to manipulate the handshake lines in order to control the radio modem's transmitter, from userspace. The transmitter should not be turned off before all characters have been transmitted. serial8250_tx_empty() was reporting that all characters were transmitted before they actually were. === Discovered in parallel with more testing and analysis by Kees Schoenmakers as follows: I ran into an NetMos 9835 serial pci board which behaves a little different than the standard. This type of expansion board is very common. "Standard" 8250 compatible devices clear the 'UART_LST_TEMT" bit together with the "UART_LSR_THRE" bit when writing data to the device. The NetMos device does it slightly different I believe that the TEMT bit is coupled to the shift register. The problem is that after writing data to the device and very quickly after that one does call serial8250_tx_empty, it returns the wrong information. My patch makes the test more robust (and solves the problem) and it does not affect the already correct devices. Alan: We may yet need to quirk this but now we know which chips we have a way to do that should we find this breaks some other 8250 clone with dodgy THRE. Signed-off-by: Dick Hollenbeck <dick@softplc.com> Signed-off-by: Alan Cox <alan@linux.intel.com> Cc: Kees Schoenmakers <k.schoenmakers@sigmae.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/serial/8250.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 524f6ab5e05c..fa3cfbc32fc2 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -81,6 +81,9 @@ static int serial_index(struct uart_port *port)
#define PASS_LIMIT 256
+#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
+
+
/*
* We default to IRQ0 for the "no irq" hack. Some
* machine types want others as well - they're free
@@ -1790,7 +1793,7 @@ static unsigned int serial8250_tx_empty(struct uart_port *port)
up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
spin_unlock_irqrestore(&up->port.lock, flags);
- return lsr & UART_LSR_TEMT ? TIOCSER_TEMT : 0;
+ return (lsr & BOTH_EMPTY) == BOTH_EMPTY ? TIOCSER_TEMT : 0;
}
static unsigned int serial8250_get_mctrl(struct uart_port *port)
@@ -1848,8 +1851,6 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state)
spin_unlock_irqrestore(&up->port.lock, flags);
}
-#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
-
/*
* Wait for transmitter & holding register to empty
*/