On 09/15/2014 10:00 AM, Frans Klaver wrote:
> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> this to about 170 overflows in 10 minutes.
Why is the threadirqs kernel boot option not sufficient?
Or conversely, shouldn't this be selectable?
Regards,
Peter Hurley
PS - To overflow the 64 byte RX FIFO at those data rates means interrupt
latency in excess of 250us?
> In practice this therefore reduces the need for hardware flow control,
> meaning the sending side doesn't have to buffer as much either.
>
> Signed-off-by: Frans Klaver <frans.klaver@xxxxxxxxx>
> ---
> drivers/tty/serial/omap-serial.c | 30 +++++++++++++++++++++++-------
> 1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 7d3f557..398139a 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -575,6 +575,20 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
> }
>
> /**
> + * serial_omap_fast_irq() - schedule interrupt handling
> + */
> +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
> +{
> + struct uart_omap_port *up = dev_id;
> + unsigned int iir = serial_in(up, UART_IIR);
> +
> + if (iir & UART_IIR_NO_INT)
> + return IRQ_NONE;
> +
> + return IRQ_WAKE_THREAD;
> +}
> +
> +/**
> * serial_omap_irq() - This handles the interrupt from one port
> * @irq: uart port irq number
> * @dev_id: uart port info
> @@ -584,7 +598,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
> struct uart_omap_port *up = dev_id;
> unsigned int iir, lsr;
> unsigned int type;
> - irqreturn_t ret = IRQ_NONE;
> int max_count = 256;
>
> spin_lock(&up->port.lock);
> @@ -595,7 +608,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
> if (iir & UART_IIR_NO_INT)
> break;
>
> - ret = IRQ_HANDLED;
> lsr = serial_in(up, UART_LSR);
>
> /* extract IRQ type from IIR register */
> @@ -634,7 +646,7 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
> pm_runtime_put_autosuspend(up->dev);
> up->port_activity = jiffies;
>
> - return ret;
> + return IRQ_HANDLED;
> }
>
> static unsigned int serial_omap_tx_empty(struct uart_port *port)
> @@ -731,15 +743,19 @@ static int serial_omap_startup(struct uart_port *port)
> /*
> * Allocate the IRQ
> */
> - retval = request_irq(up->port.irq, serial_omap_irq, up->port.irqflags,
> - up->name, up);
> + retval = request_threaded_irq(up->port.irq, serial_omap_fast_irq,
> + serial_omap_irq,
> + IRQF_ONESHOT | up->port.irqflags,
> + up->name, up);
> if (retval)
> return retval;
>
> /* Optional wake-up IRQ */
> if (up->wakeirq) {
> - retval = request_irq(up->wakeirq, serial_omap_irq,
> - up->port.irqflags, up->name, up);
> + retval = request_threaded_irq(up->wakeirq, serial_omap_fast_irq,
> + serial_omap_irq,
> + IRQF_ONESHOT | up->port.irqflags,
> + up->name, up);
> if (retval) {
> free_irq(up->port.irq, up);
> return retval;
>
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