linux-kernel - Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request

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Message-ID: <20151216090339.GX3358@xsjsorenbubuntu>
Date:	Wed, 16 Dec 2015 01:03:39 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Michal Simek <michal.simek@...inx.com>,
	<linux-serial@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	Moritz Fischer <moritz.fischer@...us.com>
Subject: Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after
 setting up the HW

On Tue, 2015-12-15 at 03:26PM -0800, Peter Hurley wrote:
> On 12/15/2015 07:41 AM, Sören Brinkmann wrote:
> > On Thu, 2015-12-10 at 01:41PM -0800, Peter Hurley wrote:
> >> On 12/05/2015 08:39 PM, Soren Brinkmann wrote:
> >>> Request_irq() should be _after_ h/w programming, otherwise an
> >>> interrupt could be triggered and in-progress before the h/w has been
> >>> setup.
> >>
> >> Slight misunderstanding. My fault; I should have been more explicit.
> >>
> >> 1. Any setup necessary for the isr not to be confused and misdirect spurious
> >>    interrupts (or hang) should be before installing the isr with request_irq()
> >>    None of this code should trigger an interrupt.
> >> 2. Clear pending interrupts
> >> 3. Install the isr with request_irq()
> >> 4. Enable interrupts
> > 
> > Isn't that what the startup function is doing now - more or less. I
> > think 3 and 4 are swapped to release the lock and then do the
> > request_irq, but I believe that should be OK.
> > The startup function configures the HW. Clears the ISR. Enables the
> > intended IRQs and then does the request_irq call.
> 
> If the driver enables interrupts before installing the isr with request_irq()
> and an interrupt occurs there will the no handler to catch it and EOI the
> device.

Really? Shouldn't the IRQ be masked in the interrupt controller until
everything is in place?

	Sören
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