Pl take a look at this patch. This is second version based and tested
on 3.19-rc2.
George Spelvin,
I'd like to add your name to Signed-off-by as well.
thanks.
On Wed, Jan 14, 2015 at 10:22 PM, Prasad Koya <prasad.koya@xxxxxxxxx> wrote:
> Patch is tested and based on 3.19-rc2.
>
> On Wed, Jan 14, 2015 at 11:47 AM, <prasad.koya@xxxxxxxxx> wrote:
>> From 859779819fe0490daaddeff5cb3cdda7a4372584 Mon Sep 17 00:00:00 2001
>> From: Prasad Koya <prasad@xxxxxxxxxx>
>> Date: Wed, 14 Jan 2015 11:07:41 -0800
>> Subject: [PATCH 1/1] tty, serial, 8250: to avoid recv fifo overrun, read rx fifo during xmit
>>
>> At slow baud rates, say 9600, it is easy to run into tty buffer overrun
>> as interrupts could get disabled for a long time. To avoid that, if
>> UART_LSR_DR is set, pick up bytes from rx fifo while waiting for tx
>> buffer to be empty. Stop buffering if port->sysrq is true or
>> oops_in_progress is set.
>>
>> George Spelvin reworked original patch quite a bit.
>>
>> Tested on 16550 UART with 16byte FIFO
>>
>> Signed-off-by: Prasad Koya <prasad@xxxxxxxxxx>
>> ---
>> drivers/tty/serial/8250/8250_core.c | 65 +++++++++++++++++++++++++++++++++----
>> drivers/tty/serial/8250/8250_fsl.c | 2 +-
>> include/linux/serial_8250.h | 3 +-
>> include/linux/serial_core.h | 2 +-
>> 4 files changed, 63 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
>> index 11c6685..a9adf9d 100644
>> --- a/drivers/tty/serial/8250/8250_core.c
>> +++ b/drivers/tty/serial/8250/8250_core.c
>> @@ -1434,9 +1434,12 @@ static void serial8250_enable_ms(struct uart_port *port)
>> * serial8250_rx_chars: processes according to the passed in LSR
>> * value, and returns the remaining LSR bits not handled
>> * by this Rx routine.
>> + * no_sysrq is normally false, but when set it indicates we should stop
>> + * processing input after receiving a break, rather than passing the
>> + * next character to uart_handle_sysrq_char.
>> */
>> unsigned char
>> -serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr)
>> +serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr, bool no_sysrq)
>> {
>> struct uart_port *port = &up->port;
>> unsigned char ch;
>> @@ -1472,8 +1475,11 @@ serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr)
>> * may get masked by ignore_status_mask
>> * or read_status_mask.
>> */
>> - if (uart_handle_break(port))
>> + if (uart_handle_break(port)) {
>> + if (no_sysrq)
>> + max_count = 0;
>> goto ignore_char;
>> + }
>> } else if (lsr & UART_LSR_PE)
>> port->icount.parity++;
>> else if (lsr & UART_LSR_FE)
>> @@ -1609,7 +1615,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
>> dma_err = up->dma->rx_dma(up, iir);
>>
>> if (!up->dma || dma_err)
>> - status = serial8250_rx_chars(up, status);
>> + status = serial8250_rx_chars(up, status, false);
>> }
>> serial8250_modem_status(up);
>> if ((!up->dma || (up->dma && up->dma->tx_err)) &&
>> @@ -1962,9 +1968,30 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state)
>> }
>>
>> /*
>> + * In some special situations, we allow console output without necessarily
>> + * locking the port. The same situations also suppress processing input
>> + * during polling output, because we aren't ready to deal with it.
>> + * So just hope the hardware FIFO can hold until interrupts are
>> + * re-enabled.
>> + */
>> +static bool emergency_situation(const struct uart_port *port)
>> +{
>> +#ifdef SUPPORT_SYSRQ
>> + return port->sysrq != 0 || oops_in_progress;
>> +#else
>> + (void)port;
>> + return oops_in_progress;
>> +#endif
>> +}
>> +
>> +/*
>> * Wait for transmitter & holding register to empty
>> + * If rx is true, then also poll for received characters if it's
>> + * safe to process them. This is only used in the SUPPORT_SYSRQ
>> + * case, and hopefully the compiler can figure out it's dead code
>> + * if that's not the case.
>> */
>> -static void wait_for_xmitr(struct uart_8250_port *up, int bits)
>> +static void __wait_for_xmitr(struct uart_8250_port *up, int bits, bool rx)
>> {
>> unsigned int status, tmout = 10000;
>>
>> @@ -1978,6 +2005,11 @@ static void wait_for_xmitr(struct uart_8250_port *up, int bits)
>> break;
>> if (--tmout == 0)
>> break;
>> +
>> + if (rx && status & (UART_LSR_DR | UART_LSR_BI) &&
>> + !emergency_situation(&up->port))
>> + serial8250_rx_chars(up, status, true);
>> +
>> udelay(1);
>> }
>>
>> @@ -1989,12 +2021,29 @@ static void wait_for_xmitr(struct uart_8250_port *up, int bits)
>> up->msr_saved_flags |= msr & MSR_SAVE_FLAGS;
>> if (msr & UART_MSR_CTS)
>> break;
>> +
>> + if (rx && !emergency_situation(&up->port)) {
>> + status = serial_in(up, UART_LSR);
>> +
>> + up->lsr_saved_flags |= status & LSR_SAVE_FLAGS;
>> + if (status & (UART_LSR_DR | UART_LSR_BI))
>> + serial8250_rx_chars(up, status, true);
>> + }
>> +
>> udelay(1);
>> touch_nmi_watchdog();
>> }
>> }
>> }
>>
>> +/*
>> + * Wait for transmitter & holding register to empty
>> + */
>> +static void wait_for_xmitr(struct uart_8250_port *up, int bits)
>> +{
>> + __wait_for_xmitr(up, bits, false);
>> +}
>> +
>> #ifdef CONFIG_CONSOLE_POLL
>> /*
>> * Console polling routines for writing and reading from the uart while
>> @@ -3168,7 +3217,7 @@ static void serial8250_console_putchar(struct uart_port *port, int ch)
>> {
>> struct uart_8250_port *up = up_to_u8250p(port);
>>
>> - wait_for_xmitr(up, UART_LSR_THRE);
>> + __wait_for_xmitr(up, UART_LSR_THRE, true);
>> serial_port_out(port, UART_TX, ch);
>> }
>>
>> @@ -3176,6 +3225,10 @@ static void serial8250_console_putchar(struct uart_port *port, int ch)
>> * Print a string to the serial port trying not to disturb
>> * any possible real use of the port...
>> *
>> + * In order to avoid dropped input if the output is longer than
>> + * the available hardware FIFO space, we try to handle incoming
>> + * characters during this polling loop.
>> + *
>> * The console_lock must be held when we get here.
>> */
>> static void
>> @@ -3214,7 +3267,7 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
>> * Finally, wait for transmitter to become empty
>> * and restore the IER
>> */
>> - wait_for_xmitr(up, BOTH_EMPTY);
>> + __wait_for_xmitr(up, BOTH_EMPTY, true);
>> serial_port_out(port, UART_IER, ier);
>>
>> /*
>> diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c
>> index c0533a5..25f0aa3 100644
>> --- a/drivers/tty/serial/8250/8250_fsl.c
>> +++ b/drivers/tty/serial/8250/8250_fsl.c
>> @@ -49,7 +49,7 @@ int fsl8250_handle_irq(struct uart_port *port)
>> lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR);
>>
>> if (lsr & (UART_LSR_DR | UART_LSR_BI))
>> - lsr = serial8250_rx_chars(up, lsr);
>> + lsr = serial8250_rx_chars(up, lsr, false);
>>
>> serial8250_modem_status(up);
>>
>> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
>> index e02acf0..8544bc5 100644
>> --- a/include/linux/serial_8250.h
>> +++ b/include/linux/serial_8250.h
>> @@ -128,7 +128,8 @@ extern void serial8250_do_pm(struct uart_port *port, unsigned int state,
>> unsigned int oldstate);
>> extern int fsl8250_handle_irq(struct uart_port *port);
>> int serial8250_handle_irq(struct uart_port *port, unsigned int iir);
>> -unsigned char serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr);
>> +unsigned char serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr,
>> + bool no_sysrq);
>> void serial8250_tx_chars(struct uart_8250_port *up);
>> unsigned int serial8250_modem_status(struct uart_8250_port *up);
>>
>> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
>> index 057038c..c93c5aa 100644
>> --- a/include/linux/serial_core.h
>> +++ b/include/linux/serial_core.h
>> @@ -410,7 +410,7 @@ uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
>> if (port->sysrq) {
>> if (ch && time_before(jiffies, port->sysrq)) {
>> handle_sysrq(ch);
>> - port->sysrq = 0;
>> + port->sysrq = 0; /* Must be AFTER handle_sysrq */
>> return 1;
>> }
>> port->sysrq = 0;
>> --
>> 1.8.1.4
>>
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