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Subject[PATCH 09/12] [Blackfin] serial driver: rework break flood anomaly handling to be more robust/realistic about what we can actually work around
Date
From: Mike Frysinger <michael.frysinger@analog.com>

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
---
drivers/serial/bfin_5xx.c | 66 ++++++++++++++++-----
include/asm-blackfin/mach-bf533/bfin_serial_5xx.h | 3 +
include/asm-blackfin/mach-bf561/bfin_serial_5xx.h | 3 +
3 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
index af84984..50aa3b2 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -206,12 +206,20 @@ int kgdb_get_debug_char(void)
}
#endif

+#if ANOMALY_05000230 && defined(CONFIG_SERIAL_BFIN_PIO)
+# define UART_GET_ANOMALY_THRESHOLD(uart) ((uart)->anomaly_threshold)
+# define UART_SET_ANOMALY_THRESHOLD(uart, v) ((uart)->anomaly_threshold = (v))
+#else
+# define UART_GET_ANOMALY_THRESHOLD(uart) 0
+# define UART_SET_ANOMALY_THRESHOLD(uart, v)
+#endif
+
#ifdef CONFIG_SERIAL_BFIN_PIO
static void bfin_serial_rx_chars(struct bfin_serial_port *uart)
{
struct tty_struct *tty = uart->port.info->tty;
unsigned int status, ch, flg;
- static int in_break = 0;
+ static struct timeval anomaly_start = { .tv_sec = 0 };
#ifdef CONFIG_KGDB_UART
struct pt_regs *regs = get_irq_regs();
#endif
@@ -244,28 +252,56 @@ static void bfin_serial_rx_chars(struct bfin_serial_port *uart)
#endif

if (ANOMALY_05000230) {
- /* The BF533 family of processors have a nice misbehavior where
- * they continuously generate characters for a "single" break.
+ /* The BF533 (and BF561) family of processors have a nice anomaly
+ * where they continuously generate characters for a "single" break.
* We have to basically ignore this flood until the "next" valid
- * character comes across. All other Blackfin families operate
- * properly though.
+ * character comes across. Due to the nature of the flood, it is
+ * not possible to reliably catch bytes that are sent too quickly
+ * after this break. So application code talking to the Blackfin
+ * which sends a break signal must allow at least 1.5 character
+ * times after the end of the break for things to stabilize. This
+ * timeout was picked as it must absolutely be larger than 1
+ * character time +/- some percent. So 1.5 sounds good. All other
+ * Blackfin families operate properly. Woo.
* Note: While Anomaly 05000230 does not directly address this,
* the changes that went in for it also fixed this issue.
+ * That anomaly was fixed in 0.5+ silicon. I like bunnies.
*/
- if (in_break) {
- if (ch != 0) {
- in_break = 0;
- ch = UART_GET_CHAR(uart);
- if (bfin_revid() < 5)
- return;
- } else
- return;
+ if (anomaly_start.tv_sec) {
+ struct timeval curr;
+ suseconds_t usecs;
+
+ if ((~ch & (~ch + 1)) & 0xff)
+ goto known_good_char;
+
+ do_gettimeofday(&curr);
+ if (curr.tv_sec - anomaly_start.tv_sec > 1)
+ goto known_good_char;
+
+ usecs = 0;
+ if (curr.tv_sec != anomaly_start.tv_sec)
+ usecs += USEC_PER_SEC;
+ usecs += curr.tv_usec - anomaly_start.tv_usec;
+
+ if (usecs > UART_GET_ANOMALY_THRESHOLD(uart))
+ goto known_good_char;
+
+ if (ch)
+ anomaly_start.tv_sec = 0;
+ else
+ anomaly_start = curr;
+
+ return;
+
+ known_good_char:
+ anomaly_start.tv_sec = 0;
}
}

if (status & BI) {
if (ANOMALY_05000230)
- in_break = 1;
+ if (bfin_revid() < 5)
+ do_gettimeofday(&anomaly_start);
uart->port.icount.brk++;
if (uart_handle_break(&uart->port))
goto ignore_char;
@@ -778,6 +814,8 @@ bfin_serial_set_termios(struct uart_port *port, struct ktermios *termios,
quot = uart_get_divisor(port, baud);
spin_lock_irqsave(&uart->port.lock, flags);

+ UART_SET_ANOMALY_THRESHOLD(uart, USEC_PER_SEC / baud * 15);
+
do {
lsr = UART_GET_LSR(uart);
} while (!(lsr & TEMT));
diff --git a/include/asm-blackfin/mach-bf533/bfin_serial_5xx.h b/include/asm-blackfin/mach-bf533/bfin_serial_5xx.h
index b619065..a1b4f4e 100644
--- a/include/asm-blackfin/mach-bf533/bfin_serial_5xx.h
+++ b/include/asm-blackfin/mach-bf533/bfin_serial_5xx.h
@@ -57,6 +57,9 @@ struct bfin_serial_port {
struct work_struct tx_dma_workqueue;
#else
struct work_struct cts_workqueue;
+# if ANOMALY_05000230
+ unsigned int anomaly_threshold;
+# endif
#endif
#ifdef CONFIG_SERIAL_BFIN_CTSRTS
int cts_pin;
diff --git a/include/asm-blackfin/mach-bf561/bfin_serial_5xx.h b/include/asm-blackfin/mach-bf561/bfin_serial_5xx.h
index b619065..a1b4f4e 100644
--- a/include/asm-blackfin/mach-bf561/bfin_serial_5xx.h
+++ b/include/asm-blackfin/mach-bf561/bfin_serial_5xx.h
@@ -57,6 +57,9 @@ struct bfin_serial_port {
struct work_struct tx_dma_workqueue;
#else
struct work_struct cts_workqueue;
+# if ANOMALY_05000230
+ unsigned int anomaly_threshold;
+# endif
#endif
#ifdef CONFIG_SERIAL_BFIN_CTSRTS
int cts_pin;
--
1.5.3.4

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