| Message ID | 1374691051-28544-2-git-send-email-sboyd@codeaurora.org (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Wed, Jul 24, 2013 at 11:37:28AM -0700, Stephen Boyd wrote: >UARTDM serial devices require us to wait for the entire TX fifo >to drain before we can change the contents of the NCF_TX >register. Furthermore, if we write any characters to the TX fifo >within the same clock cycle of changing the NCF_TX register the >NCF_TX register won't latch properly. > >To fix these issues we should read back the NCF_TX register to >delay any TX fifo accesses by a clock cycle and we should wait >for the TX fifo to drain (instead of just waiting for the fifo to >be ready to receive more characters). Failure to do so leads to >random NUL bytes interspersed in the output. > >Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> >--- > drivers/tty/serial/msm_serial.c | 14 +++++++++----- > drivers/tty/serial/msm_serial.h | 1 + > 2 files changed, 10 insertions(+), 5 deletions(-) Acked-by: David Brown <davidb@codeaurora.org>
diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c index 2c6cfb3..fa3fc67 100644 --- a/drivers/tty/serial/msm_serial.c +++ b/drivers/tty/serial/msm_serial.c @@ -50,11 +50,14 @@ struct msm_port { unsigned int old_snap_state; }; -static inline void wait_for_xmitr(struct uart_port *port, int bits) +static inline void wait_for_xmitr(struct uart_port *port) { - if (!(msm_read(port, UART_SR) & UART_SR_TX_EMPTY)) - while ((msm_read(port, UART_ISR) & bits) != bits) - cpu_relax(); + while (!(msm_read(port, UART_SR) & UART_SR_TX_EMPTY)) { + if (msm_read(port, UART_ISR) & UART_ISR_TX_READY) + break; + udelay(1); + } + msm_write(port, UART_CR_CMD_RESET_TX_READY, UART_CR); } static void msm_stop_tx(struct uart_port *port) @@ -194,8 +197,9 @@ static void handle_rx(struct uart_port *port) static void reset_dm_count(struct uart_port *port) { - wait_for_xmitr(port, UART_ISR_TX_READY); + wait_for_xmitr(port); msm_write(port, 1, UARTDM_NCF_TX); + msm_read(port, UARTDM_NCF_TX); } static void handle_tx(struct uart_port *port) diff --git a/drivers/tty/serial/msm_serial.h b/drivers/tty/serial/msm_serial.h index e4acef5..15c186e 100644 --- a/drivers/tty/serial/msm_serial.h +++ b/drivers/tty/serial/msm_serial.h @@ -71,6 +71,7 @@ #define UART_CR_CMD_RESET_RFR (14 << 4) #define UART_CR_CMD_PROTECTION_EN (16 << 4) #define UART_CR_CMD_STALE_EVENT_ENABLE (80 << 4) +#define UART_CR_CMD_RESET_TX_READY (3 << 8) #define UART_CR_TX_DISABLE (1 << 3) #define UART_CR_TX_ENABLE (1 << 2) #define UART_CR_RX_DISABLE (1 << 1)
UARTDM serial devices require us to wait for the entire TX fifo to drain before we can change the contents of the NCF_TX register. Furthermore, if we write any characters to the TX fifo within the same clock cycle of changing the NCF_TX register the NCF_TX register won't latch properly. To fix these issues we should read back the NCF_TX register to delay any TX fifo accesses by a clock cycle and we should wait for the TX fifo to drain (instead of just waiting for the fifo to be ready to receive more characters). Failure to do so leads to random NUL bytes interspersed in the output. Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> --- drivers/tty/serial/msm_serial.c | 14 +++++++++----- drivers/tty/serial/msm_serial.h | 1 + 2 files changed, 10 insertions(+), 5 deletions(-)