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

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Message-ID: <56717745.3060306@hurleysoftware.com>
Date:	Wed, 16 Dec 2015 06:37:57 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Sören Brinkmann <soren.brinkmann@...inx.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 12/16/2015 01:03 AM, Sören Brinkmann wrote:
> 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?

Sorry, I'm used to shared interrupts, where that isn't the case.

Regards,
Peter Hurley

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