Re: [patch 12/14] ACPI: Clear GPE before disabling it

["William Morrow" <William.Morrow@amd.com>]

Moore, Robert wrote:

>Worse, the GPE is already cleared in the edge case, at the start of the
>GPE dispatch function:
>
>    /*
>     * If edge-triggered, clear the GPE status bit now.  Note that
>     * level-triggered events are cleared after the GPE is serviced.
>     */
>    if ((GpeEventInfo->Flags & ACPI_GPE_XRUPT_TYPE_MASK) ==
>            ACPI_GPE_EDGE_TRIGGERED)
>    {
>        Status = AcpiHwClearGpe (GpeEventInfo);
>        if (ACPI_FAILURE (Status))
>        {
>            ACPI_EXCEPTION ((AE_INFO, Status,
>                "Unable to clear GPE[%2X]", GpeNumber));
>            return_UINT32 (ACPI_INTERRUPT_NOT_HANDLED);
>        }
>    }
>
>  
>
Sorry for the late reply, but I have not looked at this for some time.
I had to re-examine this issue.

The interrupt type is tagged as level triggered in this case.

The dispatch handler is ACPI_GPE_DISPATCH_METHOD and so the
method is queued, but the interrupt is not cleared (it is disabled instead).
In this hw, that is all that happens.  It is disabled but not cleared.
The original comment would lead me to think that the prevailing thought
was that disabling the gpe implied clearing the interrupt status.  That is
not the case in this hw environment, and the result is the interrupt storm.

Although this handler is artfully done,  the architecture of this
handler is unusual in that most interrupt handlers field status
and clear the offending event at once, then process the new input.
This handler is coded in a way that seems to indicate that interrupt
status is possible when events are not enabled, but is not willing to
clear them - again indicating that the hw design is required to block
interrupts if the event has been disabled, but the interrupt status is
not clear.  If that is true - then this code has no effect, or is another
case which can result in an interrupt storm.

    /* Check if there is anything active at all in this register */

    enabled_status_byte = (u8) (status_reg & enable_reg);
    if (!enabled_status_byte) {
      /* No active GPEs in this register, move on */
      continue;
    }

Additionally, any error return which prevents the interrupt
source from being cleared will result in an interrupt storm.
This occurs several times.

The comment:

/*
 * Execute the method associated with the GPE
 * NOTE: Level-triggered GPEs are cleared after the method completes.
 */
 Status = AcpiOsExecute (OSL_GPE_HANDLER,
             AcpiEvAsynchExecuteGpeMethod, GpeEventInfo);

is alarming, since it documents that the interrupt is active and
expects the OS to be able to schedule with pending interrupts.

My personal preference is that the code be modified to work in
the more traditional way, but since that would be a large change
and this produced the desired result - I opted for the minimum
coding distance change.


If there are any other materials you need to evaluate this change, let 
me know.
I hope this addresses your point.  I am sort of renowned for being a 
little askew
when trying to explain myself.

Thanks for your attention!
morrow

>
>  
>
>>-----Original Message-----
>>From: Moore, Robert
>>Sent: Wednesday, August 16, 2006 2:50 PM
>>To: 'akpm@osdl.org'; Brown, Len
>>Cc: linux-acpi@vger.kernel.org; william.morrow@amd.com;
>>jordan.crouse@amd.com; Yu, Luming
>>Subject: RE: [patch 12/14] ACPI: Clear GPE before disabling it
>>
>>How does this patch relate to level-triggered GPEs, where we have the
>>following comment in the code just after the patch:
>>
>>        /*
>>         * Execute the method associated with the GPE
>>         * NOTE: Level-triggered GPEs are cleared after the method
>>completes.
>>         */
>>        Status = AcpiOsExecute (OSL_GPE_HANDLER,
>>                    AcpiEvAsynchExecuteGpeMethod, GpeEventInfo);
>>
>>    
>>
>>>-----Original Message-----
>>>From: akpm@osdl.org [mailto:akpm@osdl.org]
>>>Sent: Monday, August 14, 2006 10:38 PM
>>>To: Brown, Len
>>>Cc: linux-acpi@vger.kernel.org; akpm@osdl.org;
>>>      
>>>
>william.morrow@amd.com;
>  
>
>>>jordan.crouse@amd.com; Yu, Luming; Moore, Robert
>>>Subject: [patch 12/14] ACPI: Clear GPE before disabling it
>>>
>>>From: William Morrow <william.morrow@amd.com>
>>>
>>>On some BIOSen, the GPE bit will remain set even if it is disabled,
>>>resulting in a interrupt storm.  This patch clears the bit before
>>>disabling
>>>it.
>>>
>>>Signed-off-by: William Morrow <william.morrow@amd.com>
>>>Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
>>>Cc: "Yu, Luming" <luming.yu@intel.com>
>>>Cc: "Brown, Len" <len.brown@intel.com>
>>>Cc: "Moore, Robert" <robert.moore@intel.com>
>>>Signed-off-by: Andrew Morton <akpm@osdl.org>
>>>---
>>>
>>> drivers/acpi/events/evgpe.c |   14 +++++++++++++-
>>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>>diff -puN
>>>      
>>>
>drivers/acpi/events/evgpe.c~acpi-clear-gpe-before-disabling-it
>  
>
>>>drivers/acpi/events/evgpe.c
>>>--- a/drivers/acpi/events/evgpe.c~acpi-clear-gpe-before-disabling-it
>>>+++ a/drivers/acpi/events/evgpe.c
>>>@@ -677,10 +677,22 @@ acpi_ev_gpe_dispatch(struct acpi_gpe_eve
>>> 	case ACPI_GPE_DISPATCH_METHOD:
>>>
>>> 		/*
>>>-		 * Disable GPE, so it doesn't keep firing before the
>>>      
>>>
>method
>  
>
>>>has a
>>>+		 * Clear GPE, so it doesn't keep firing before the
>>>      
>>>
>method has
>  
>
>>>a
>>> 		 * chance to run.
>>> 		 */
>>>+		status = acpi_hw_clear_gpe(gpe_event_info);
>>>+		if (ACPI_FAILURE(status)) {
>>>+			ACPI_EXCEPTION((AE_INFO, status,
>>>+					"Unable to clear GPE[%2X]",
>>>+					gpe_number));
>>>+			return_UINT32(ACPI_INTERRUPT_NOT_HANDLED);
>>>+		}
>>>+		/*
>>>+		 * Disable GPE, so it doesn't keep happen again.
>>>+		 */
>>>+
>>> 		status = acpi_ev_disable_gpe(gpe_event_info);
>>>+
>>> 		if (ACPI_FAILURE(status)) {
>>> 			ACPI_EXCEPTION((AE_INFO, status,
>>> 					"Unable to disable GPE[%2X]",
>>>_
>>>      
>>>
>
>
>  
>