linux-kernel - Re: [PATCH 3/3] Revert "ACPI,PCI,IRQ: remove SCI penalize function"

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Date:   Tue, 4 Oct 2016 10:10:12 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-acpi@...r.kernel.org, rjw@...ysocki.net, bhelgaas@...gle.com,
        ravikanth.nalla@....com, linux@...nbow-software.org,
        timur@...eaurora.org, cov@...eaurora.org, jcm@...hat.com,
        alex.williamson@...hat.com, linux-pci@...r.kernel.org,
        agross@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, wim@....tudelft.nl,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Revert "ACPI,PCI,IRQ: remove SCI penalize function"

On 10/4/2016 3:23 AM, Thomas Gleixner wrote:
> On Sat, 1 Oct 2016, Sinan Kaya wrote:
> 
>> This reverts commit 9e5ed6d1fb87 ("ACPI,PCI,IRQ: remove SCI penalize
>> function"). SCI penalty API was replaced by the runtime penalty calculation
>> based on the value of acpi_gbl_FADT.sci_interrupt.
> 
> This does more than only reverting said commit ....

The SCI function was removed in two steps (first refactor and then remove). 
I was trying to do the revert at one step. I can divide into two if it makes
it better.

>  
>> acpi_gbl_FADT.sci_interrupt type does not get updated at the right time
>> for some platforms and results in incorrect penalty assignment for PCI
>> IRQs as irq_get_trigger_type returns the wrong type.
> 
> And the obvious question is: Why does irq_get_trigger_type() return the
> wrong type?

Here is some history:

I now remember that Bjorn indicated the race condition possibility in this thread
here.

https://lkml.org/lkml/2016/3/8/640

My understanding is that register_gsi function delivers the IRQ found in the ACPI table
to the interrupt controller driver.

Penalties are calculated before a link object is enabled to find out which interrupt
has the least number of users. By the time penalties are calculated, the IRQ is not
registered yet and it returns the wrong type.

> 
> What's the root cause of this problem? Your changelog does not tell
> anything.

If you are OK with the above description, I can add this to the commit message.


> 
> Thanks,
> 
> 	tglx
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-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.