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Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after setting up the HW

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  Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after  setting up the HW Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-12-15 16:50 +0100
    Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after  setting up the HW Peter Hurley <peter@hurleysoftware.com> - 2015-12-16 00:30 +0100
      Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after  setting up the HW Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-12-16 10:10 +0100
        Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after  setting up the HW Peter Hurley <peter@hurleysoftware.com> - 2015-12-16 15:40 +0100
          Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after  setting up the HW Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-12-17 11:10 +0100

#1292303 — Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after setting up the HW

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.

> 
> For extra safety, first disable interrupts before starting h/w programming.

It's done within spin_lock_irqsave, which gives us at least locally
disabled IRQs. I guess we could add a disabling all IRQs in the UART
core, but it should not really be necessary.

> 
> I would do the v5 series in the same order as the v3 series only up to
> what I reviewed. Then do another series with the remainder plus new changes, ok?

Sure.

	Sören

> 
> Regards,
> Peter Hurley
> 
> > Reported-by: Peter Hurley <peter@hurleysoftware.com>
> > Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
> > ---
> > v4:
> >  - this patch has been added. Thanks to Peter for pointing it out and providing
> >    commit message
> > ---
> >  drivers/tty/serial/xilinx_uartps.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> > index 6ffd3bbe3e18..1e9053656610 100644
> > --- a/drivers/tty/serial/xilinx_uartps.c
> > +++ b/drivers/tty/serial/xilinx_uartps.c
> > @@ -759,12 +759,7 @@ static void cdns_uart_set_termios(struct uart_port *port,
> >  static int cdns_uart_startup(struct uart_port *port)
> >  {
> >  	unsigned long flags;
> > -	unsigned int retval = 0, status = 0;
> > -
> > -	retval = request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME,
> > -								(void *)port);
> > -	if (retval)
> > -		return retval;
> > +	unsigned int status = 0;
> >  
> >  	spin_lock_irqsave(&port->lock, flags);
> >  
> > @@ -818,7 +813,7 @@ static int cdns_uart_startup(struct uart_port *port)
> >  
> >  	spin_unlock_irqrestore(&port->lock, flags);
> >  
> > -	return retval;
> > +	return request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME, port);
> >  }
> >  
> >  /**
> > 
> 
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#1292640

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.


>> For extra safety, first disable interrupts before starting h/w programming.
> 
> It's done within spin_lock_irqsave, which gives us at least locally
> disabled IRQs. I guess we could add a disabling all IRQs in the UART
> core, but it should not really be necessary.

Similar issue.

What I mean is to mask interrupts from this device so that h/w programming
doesn't accidentally trigger an interrupt for which no isr is installed.

It's a bit overkill; that's why I said "extra safety".

Regards,
Peter Hurley


>> I would do the v5 series in the same order as the v3 series only up to
>> what I reviewed. Then do another series with the remainder plus new changes, ok?
> 
> Sure.
> 
> 	Sören
> 
>>
>> Regards,
>> Peter Hurley
>>
>>> Reported-by: Peter Hurley <peter@hurleysoftware.com>
>>> Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
>>> ---
>>> v4:
>>>  - this patch has been added. Thanks to Peter for pointing it out and providing
>>>    commit message
>>> ---
>>>  drivers/tty/serial/xilinx_uartps.c | 9 ++-------
>>>  1 file changed, 2 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
>>> index 6ffd3bbe3e18..1e9053656610 100644
>>> --- a/drivers/tty/serial/xilinx_uartps.c
>>> +++ b/drivers/tty/serial/xilinx_uartps.c
>>> @@ -759,12 +759,7 @@ static void cdns_uart_set_termios(struct uart_port *port,
>>>  static int cdns_uart_startup(struct uart_port *port)
>>>  {
>>>  	unsigned long flags;
>>> -	unsigned int retval = 0, status = 0;
>>> -
>>> -	retval = request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME,
>>> -								(void *)port);
>>> -	if (retval)
>>> -		return retval;
>>> +	unsigned int status = 0;
>>>  
>>>  	spin_lock_irqsave(&port->lock, flags);
>>>  
>>> @@ -818,7 +813,7 @@ static int cdns_uart_startup(struct uart_port *port)
>>>  
>>>  	spin_unlock_irqrestore(&port->lock, flags);
>>>  
>>> -	return retval;
>>> +	return request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME, port);
>>>  }
>>>  
>>>  /**
>>>
>>

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#1292836

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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#1292989

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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#1293730

On Wed, 2015-12-16 at 06:37AM -0800, Peter Hurley wrote:
> 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.

Ahh, I didn't have to deal with such cases yet. Makes sense though.

	Thanks,
	Sören
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