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

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Date:	Wed, 20 Aug 2014 11:06:05 -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 Wed, Aug 20, 2014 at 08:40:28AM +0200, Frans Klaver wrote:
> On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
> > 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.
> 
> I'll have a look at that series. Thanks for pointing it out.
> 
> > >  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).
> 
> Given the work that's been done on the 8250 based driver, what are the
> short-term chances omap-serial will be dropped? I'd be happy to improve
> here if it makes sense to do so. If the 8250 based driver is going to
> replace omap-serial anyway on the short term, I don't see the point of
> further developing this patch. The others would still make sense in my
> opinion.

if we find a way to maintain the same ttyO* naming scheme and make it
coexist with ttyS* naming, then we could drop as soon as 8250_omap is
ready for prime time.

-- 
balbi

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