linux-kernel - Re: [RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

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Message-ID: <20140819185701.GC22003@saruman.home>
Date:	Tue, 19 Aug 2014 13:57:02 -0500
From:	Felipe Balbi <balbi@...com>
To:	Frans Klaver <frans.klaver@...ns.com>
CC:	Felipe Balbi <balbi@...com>, Tony Lindgren <tony@...mide.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexey Pelykh <alexey.pelykh@...il.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Frans Klaver <fransklaver@...il.com>,
	<linux-serial@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

On Tue, Aug 19, 2014 at 02:14:47PM +0200, 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.

Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
support ? That should help you a lot.

> 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@...ns.com>
> ---
>  drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 14a0167..57664b9 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -575,6 +575,21 @@ 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;
> +
> +	disable_irq_nosync(up->port.irq);

NAK. Either use IRQF_ONESHOT or actually mask the IRQs at the device's
registers (basically clearing IER).

-- 
balbi

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