Date:	Mon, 7 Mar 2016 11:55:43 -0500
From:	Sinan Kaya <okaya@...eaurora.org>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	linux-acpi@...r.kernel.org, timur@...eaurora.org,
	cov@...eaurora.org, linux-pci@...r.kernel.org,
	ravikanth.nalla@....com, lenb@...nel.org, harish.k@....com,
	ashwin.reghunandanan@....com, bhelgaas@...gle.com,
	rjw@...ysocki.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] acpi, pci, irq: account for early penalty assignment

On 3/4/2016 1:09 PM, Bjorn Helgaas wrote:
> On Thu, Mar 03, 2016 at 12:29:01PM -0500, Sinan Kaya wrote:
>> On 3/3/2016 10:12 AM, Sinan Kaya wrote:
>>> On 3/3/2016 10:10 AM, Bjorn Helgaas wrote:
>>>> That was my idea, but your minimal patch from last night looks awfully
>>>> attractive, and maybe it's not worth moving it to arch/x86.  I do think we
>>>> could simplify the code significantly by getting rid of the kzalloc and
>>>> acpi_irq_penalty_list from acpi_irq_set_penalty().  How about pushing on
>>>> that a little bit first, and see what it looks like then?
>>>
>>> OK. Let me go that direction.
>>>
>>
>> How about this?
>>
>> -- 
>> Sinan Kaya
>> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
> 
>> From 6cc33747feb469fe4da2088f34e2c875a36f58f4 Mon Sep 17 00:00:00 2001
>> From: Sinan Kaya <okaya@...eaurora.org>
>> Date: Thu, 3 Mar 2016 10:14:22 -0500
>> Subject: [PATCH] acpi,pci,irq: account for early penalty assignment
>>
>> ---
>>  drivers/acpi/pci_link.c | 77 ++++++++++++++++++++++++++++++-------------------
>>  1 file changed, 47 insertions(+), 30 deletions(-)
>>
>> diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
>> index fa28635..09eea42 100644
>> --- a/drivers/acpi/pci_link.c
>> +++ b/drivers/acpi/pci_link.c
>> @@ -87,6 +87,7 @@ struct acpi_pci_link {
>>
>>  static LIST_HEAD(acpi_link_list);
>>  static DEFINE_MUTEX(acpi_link_lock);
>> +static int sci_irq, sci_irq_penalty;
>>
>>  /* --------------------------------------------------------------------------
>>                              PCI Link Device Management
>> @@ -466,56 +467,71 @@ static int acpi_irq_isa_penalty[ACPI_MAX_ISA_IRQ] = {
>>  	PIRQ_PENALTY_ISA_USED,		/* IRQ15 ide1 */
>>  };
>>
>> -struct irq_penalty_info {
>> -	int irq;
>> -	int penalty;
>> -	struct list_head node;
>> -};
>> +static int acpi_irq_pci_sharing_penalty(int irq)
>> +{
>> +	struct acpi_pci_link *link;
>> +	int penalty = 0;
>> +	bool found = false;
>> +
>> +	list_for_each_entry(link, &acpi_link_list, list) {
>> +		/*
>> +		 * If a link is active, penalize its IRQ heavily
>> +		 * so we try to choose a different IRQ.
>> +		 */
>> +		if (link->irq.active && link->irq.active == irq) {
>> +			penalty += PIRQ_PENALTY_PCI_USING;
>> +			found = true;
>> +		} else {
>> +			int i;
>> +
>> +			/*
>> +			 * If a link is inactive, penalize the IRQs it
>> +			 * might, but not as severely.
> 
> s/might/might use/
OK

> 
>> +			 */
>> +			for (i = 0; i < link->irq.possible_count; i++) {
>> +				if (link->irq.possible[i] == irq) {
>> +					penalty += PIRQ_PENALTY_PCI_POSSIBLE /
>> +						link->irq.possible_count;
>> +					found = true;
>> +				}
>> +			}
>> +		}
>> +	}
>>
>> -static LIST_HEAD(acpi_irq_penalty_list);
>> +	if (found)
>> +		return penalty;
>> +
>> +	return PIRQ_PENALTY_PCI_AVAILABLE;
> 
> It's a nit, but I don't think "#define PIRQ_PENALTY_PCI_AVAILABLE 0"
> adds any readability.  If we dropped that, you could get rid of
> "found" as well, and simply "return penalty" here.
> 

Right, I never looked at what PIRQ_PENALTY_PCI_AVAILABLE value is. I was trying to 
match what current code is doing. I'll get rid of PIRQ_PENALTY_PCI_AVAILABLE 
altogether.


>> +}
>>
>>  static int acpi_irq_get_penalty(int irq)
>>  {
>> -	struct irq_penalty_info *irq_info;
>> -
>>  	if (irq < ACPI_MAX_ISA_IRQ)
>>  		return acpi_irq_isa_penalty[irq];
>>
>> -	list_for_each_entry(irq_info, &acpi_irq_penalty_list, node) {
>> -		if (irq_info->irq == irq)
>> -			return irq_info->penalty;
>> -	}
>> +	if (irq == sci_irq)
>> +		return sci_irq_penalty;
>>
>> -	return 0;
>> +	return acpi_irq_pci_sharing_penalty(irq);
> 
> I think there are two issues here that should be teased apart a bit
> more:
> 
>   1) Trigger settings: If the IRQ is configured as anything other than
>   level-triggered, active-low, we can't use it at all for a PCI
>   interrupt, and we should return an "infinite" penalty.  We currently
>   increase the penalty for the SCI IRQ if it's not level/low, but
>   doesn't it apply to *all* IRQs, not just the SCI IRQ?
>   

It makes sense for SCI as it is Intel specific.

Unfortunately, this cannot be done in an arch independent way. Of course,
ARM had to implement its own thing. While level-triggered, active-low is
good for intel world, it is not for the ARM world. ARM uses active-high
level triggered.

Of course, we could do something like this and check for level.

+       if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
+               polarity = ACPI_ACTIVE_HIGH;
+

Let me know what you think.

>   It looks like we do something similar in the pcibios_lookup_irq()
>   loop that uses can_request_irq().  If we used can_request_irq() in
>   pci_link.c, would that mean we could get rid of the SCI
>   trigger/polarity stuff and just keep track of the SCI IRQ?  I don't
>   know whether the SCI IRQ is hooked into whatever can_request_irq()
>   uses, but it seems like it *should* be.

Sorry, you lost me here. We are only tracking sci_irq and sci_penalty. 
Do you want to add an additional check here? something like this?

        if (trigger != ACPI_MADT_TRIGGER_LEVEL ||
-           polarity != ACPI_MADT_POLARITY_ACTIVE_LOW)
+           polarity != ACPI_MADT_POLARITY_ACTIVE_LOW) &&
+           !can_request_irq(irq, IRQF_SHARED | IRQF_TRIGGER_LOW))

> 
>   2) Sharing with other devices: It seems useful to me to accumulate
>   the penalties because even an IRQ in the 0-15 range might be used by
>   PCI devices.  Wouldn't we want to count those users in addition to
>   whatever ISA users there might be?  E.g., something like this:
> 
>     penalty = 0;
> 
>     if (irq < ACPI_MAX_ISA_IRQ)
>       penalty += acpi_irq_isa_penalty[irq];
> 
>     if (irq == sci_irq)
>       penalty += PIRQ_PENALTY_PCI_USING;
> 
>     penalty += acpi_irq_pci_sharing_penalty(irq);
>     return penalty;
> 
>>  }

Sure, makes sense. Changed it like above.

>>
>>  static int acpi_irq_set_penalty(int irq, int new_penalty)
>>  {
>> -	struct irq_penalty_info *irq_info;
>> -
>>  	/* see if this is a ISA IRQ */
>>  	if (irq < ACPI_MAX_ISA_IRQ) {
>>  		acpi_irq_isa_penalty[irq] = new_penalty;
>>  		return 0;
>>  	}
>>
>> -	/* next, try to locate from the dynamic list */
>> -	list_for_each_entry(irq_info, &acpi_irq_penalty_list, node) {
>> -		if (irq_info->irq == irq) {
>> -			irq_info->penalty  = new_penalty;
>> -			return 0;
>> -		}
>> +	if (irq == sci_irq) {
>> +		sci_irq_penalty = new_penalty;
>> +		return 0;
>>  	}
>>
>> -	/* nope, let's allocate a slot for this IRQ */
>> -	irq_info = kzalloc(sizeof(*irq_info), GFP_KERNEL);
>> -	if (!irq_info)
>> -		return -ENOMEM;
>> -
>> -	irq_info->irq = irq;
>> -	irq_info->penalty = new_penalty;
>> -	list_add_tail(&irq_info->node, &acpi_irq_penalty_list);
>> -
>> +	/*
>> +	 * This is the remaining PCI IRQs. They are calculated on the
>> +	 * flight in acpi_irq_get_penalty function.
>> +	 */
>>  	return 0;
>>  }
> 
> If we adopt the idea that we compute the penalties on the fly in
> acpi_irq_get_penalty(), I don't think we need acpi_irq_penalty_init()
> any more.  It does basically the same thing acpi_irq_get_penalty()
> would do, and it's confusing to do it twice.

Agreed, I was going to take it out. I didn't want to get on it yet. Emptied
the function now.

> 
> The acpi_irq_add_penalty() call in acpi_pci_link_allocate() should go
> away for the same reason.

got it.

> 
> The acpi_irq_add_penalty() call in acpi_penalize_sci_irq() should go
> away (assuming we can use can_request_irq() or something similar to
> validate trigger settings).

@@ -917,13 +880,15 @@ void acpi_penalize_sci_irq(int irq, int trigger, int polarity)
                return;

        sci_irq = irq;
+
        if (trigger != ACPI_MADT_TRIGGER_LEVEL ||
-           polarity != ACPI_MADT_POLARITY_ACTIVE_LOW)
+           polarity != ACPI_MADT_POLARITY_ACTIVE_LOW) &&
+           !can_request_irq(irq, IRQF_SHARED | IRQF_TRIGGER_LOW))
                penalty = PIRQ_PENALTY_ISA_ALWAYS;
        else
                penalty = PIRQ_PENALTY_PCI_USING;

-       acpi_irq_add_penalty(irq, penalty);
+       sci_penalty = penalty;

> 
> I think acpi_irq_add_penalty() itself could go away, since the only
> remaining user would be the command-line processing, which could just
> set the penalty directly.

OK, this is how I changed acpi_penalize_isa_irq.

@@ -894,8 +857,8 @@ static int __init acpi_irq_penalty_update(char *str, int used)
 void acpi_penalize_isa_irq(int irq, int active)
 {
        if (irq >= 0)
-               acpi_irq_add_penalty(irq, active ?
-                       PIRQ_PENALTY_ISA_USED : PIRQ_PENALTY_PCI_USING);
+               acpi_irq_isa_penalty[irq] = active ?
+                       PIRQ_PENALTY_ISA_USED : PIRQ_PENALTY_PCI_USING;
 }


> 
>>
>> @@ -900,6 +916,7 @@ void acpi_penalize_sci_irq(int irq, int trigger, int polarity)
>>  	if (irq < 0)
>>  		return;
>>
>> +	sci_irq = irq;
> 
> Possibly acpi_penalize_sci_irq() itself could go away, since all we
> really need is the SCI IRQ, and we might be able to just use
> acpi_gbl_FADT.sci_interrupt (I'm not 100% sure sci_interrupt is
> identical to a Linux IRQ number; we'd have to check that).

Is SCI IRQ exclusive in general? We are now keeping track of SCI IRQ and 
adding penalty when irq matches sci_irq in get_penalty function. 

How do we make sci_irq_penalty and acpi_penalize_sci_irq disappear?

> 
>>  	if (trigger != ACPI_MADT_TRIGGER_LEVEL ||
>>  	    polarity != ACPI_MADT_POLARITY_ACTIVE_LOW)
>>  		penalty = PIRQ_PENALTY_ISA_ALWAYS;
>> --
>> 1.8.2.1
>>
> 
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> 


-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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