linux-kernel - Re: Possible bug in 8250.c

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Date:	Fri, 19 Aug 2011 17:58:24 -0700
From:	Ivica Mikec <mikeci@....org>
To:	"Jiri Slaby" <jslaby@...e.cz>, <mikeci@....org>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Possible bug in 8250.c

I traced the function using jtag debugger. 

UART is not sharing interrupts:
========================================= Console ========================
Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled
serial8250.0: ttyS0 at MMIO 0xae023400 (irq = 53) is a 16550A
console [ttyS0] enabled, bootconsole disabled
=========================================================================
And /proc/interrupts:

=========================================================================
cat /proc/interrupts
              CPU0
 53:       4534                XXXXX  serial
 56:         12                   XXXXX  phy_interrupt
153:   20262068          XXXXX  timer
ERR:          0
=========================================================================

So in first iteration, interrupt is cleared, and in second, function will execute:

          } else if (end == NULL)
                        end = l;

which will terminate the loop, but the return code will be IRQ_RETVAL(0).




On Fri 19/08/11 12:01 , Jiri Slaby <jslaby@...e.cz> wrote:

> On 08/19/2011 07:44 PM, Ivica Mikec wrote:
> > 
> > Hi!
> > 
> > 
> > I noticed a problem in 8250.c. 
> > 
> > My board has only one UART port, and is 16550 compatible, so in function
> serial8250_interrupt I see that serial_in function is called twice. Second
> time, code "else if (end == NULL)" is executed and function return
> IRQ_NONE. This causes an entry in /proc/irq/spurious:
> > 
> > count 239
> > unhandled 1
> > last_unhandled 4294700846 ms
> > 
> > But this is not a spurious interrupt.
> 
> How did you find out? Have you checked that the port signals that it
> raised an interrupt? I.e. does it go through the 'if (!(iir &
> UART_IIR_NO_INT))' branch?
> 
> What other devices are bound to the same interrupt? Attach
> /proc/interrupts.
> 
> regards,
> -- 
> js
> suse labs
> 
> 
> 
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