linux-kernel - Re: [PATCH v2 5/5] irqchip/irq-bcm7038-l1: Support brcm,int-fwd-mask

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Message-ID: <8b0f18ef-7b72-e6fd-9930-0f698ced270b@gmail.com>
Date:   Mon, 23 Sep 2019 07:39:36 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Marc Zyngier <maz@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Cernekee <cernekee@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] irqchip/irq-bcm7038-l1: Support brcm,int-fwd-mask



On 9/23/2019 1:52 AM, Marc Zyngier wrote:
> On 22/09/2019 20:08, Florian Fainelli wrote:
>>
>>
>> On 9/22/2019 5:38 AM, Marc Zyngier wrote:
>>> On Fri, 13 Sep 2019 12:15:42 -0700
>>> Florian Fainelli <f.fainelli@...il.com> wrote:
>>>
>>>> On some specific chips like 7211 we need to leave some interrupts
>>>> untouched/forwarded to the VPU which is another agent in the system
>>>> making use of that interrupt controller hardware (goes to both ARM GIC
>>>> and VPU L1 interrupt controller). Make that possible by using the
>>>> existing brcm,int-fwd-mask property.
>>>>
>>>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>>>> ---
>>>>  drivers/irqchip/irq-bcm7038-l1.c | 15 +++++++++++++--
>>>>  1 file changed, 13 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-bcm7038-l1.c b/drivers/irqchip/irq-bcm7038-l1.c
>>>> index 0673a44bbdc2..811a34201dd4 100644
>>>> --- a/drivers/irqchip/irq-bcm7038-l1.c
>>>> +++ b/drivers/irqchip/irq-bcm7038-l1.c
>>>> @@ -44,6 +44,7 @@ struct bcm7038_l1_chip {
>>>>  	struct list_head	list;
>>>>  	u32			wake_mask[MAX_WORDS];
>>>>  #endif
>>>> +	u32			irq_fwd_mask[MAX_WORDS];
>>>>  	u8			affinity[MAX_WORDS * IRQS_PER_WORD];
>>>>  };
>>>>  
>>>> @@ -265,6 +266,7 @@ static int __init bcm7038_l1_init_one(struct device_node *dn,
>>>>  	resource_size_t sz;
>>>>  	struct bcm7038_l1_cpu *cpu;
>>>>  	unsigned int i, n_words, parent_irq;
>>>> +	int ret;
>>>>  
>>>>  	if (of_address_to_resource(dn, idx, &res))
>>>>  		return -EINVAL;
>>>> @@ -278,6 +280,14 @@ static int __init bcm7038_l1_init_one(struct device_node *dn,
>>>>  	else if (intc->n_words != n_words)
>>>>  		return -EINVAL;
>>>>  
>>>> +	ret = of_property_read_u32_array(dn , "brcm,int-fwd-mask",
>>>
>>> What is the exact meaning of "fwd"? Forward? FirmWare Dementia?
>>
>> Here it is meant to be "forward", we have defined this property name
>> before for irq-bcm7120-l2.c and felt like reusing the same name to avoid
>> multiplying properties would be appropriate, see patch #4. If you prefer
>> something named brcm,firmware-configured-mask, let me know.
> 
> It's just a name, but I found it a bit confusing. Bah, never mind.
> 
>>>
>>>> +					 intc->irq_fwd_mask, n_words);
>>>> +	if (ret != 0 && ret != -EINVAL) {
>>>> +		/* property exists but has the wrong number of words */
>>>> +		pr_err("invalid brcm,int-fwd-mask property\n");
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>>  	cpu = intc->cpus[idx] = kzalloc(sizeof(*cpu) + n_words * sizeof(u32),
>>>>  					GFP_KERNEL);
>>>>  	if (!cpu)
>>>> @@ -288,8 +298,9 @@ static int __init bcm7038_l1_init_one(struct device_node *dn,
>>>>  		return -ENOMEM;
>>>>  
>>>>  	for (i = 0; i < n_words; i++) {
>>>> -		l1_writel(0xffffffff, cpu->map_base + reg_mask_set(intc, i));
>>>> -		cpu->mask_cache[i] = 0xffffffff;
>>>> +		l1_writel(0xffffffff & ~intc->irq_fwd_mask[i],
>>>> +			  cpu->map_base + reg_mask_set(intc, i));
>>>> +		cpu->mask_cache[i] = 0xffffffff & ~intc->irq_fwd_mask[i];
>>>
>>> I seem to remember that (0xffffffff & whatever) == whatever, as long as
>>> 'whatever' is a 32bit quantity. So what it this for?
>>
>> It is 0xffff_ffff & ~whatever here.
> 
> Which doesn't change anything.
> 
>> In the absence of this property
>> being specified, the data is all zeroed out, so we would have
>> 0xffff_ffff & 0xffff_ffff which is 0xffff_ffff. If this property is
>> specified, we would have one more or bits set, and it would be e.g.:
>> 0x100 so we would have 0xffff_ffff & ~(0x100) = 0xffff_feff which is
>> what we would want here to preserve whatever the firmware has already
>> configured.
> 
> OK, I must be stupid:
> 
> #include <stdio.h>
> 
> int main(int argc, char *argv[])
> {
> 	unsigned int v = 0x100;
> 	printf ("%x\n", ~v);
> }
> maz@...thy-habit$ ./x
> fffffeff
> 
> You might as well OR it with zeroes, if you want.

Not sure I understand your point here.

We used to write 0xffff_ffff to both the hardware and the mask cache to
have all interrupts masked by default. Now we want to have some bits
optionally set to 0 (unmasked), based on the brcm,int-fwd-mask property,
which is what this patch achieves (or tries to). If we write, say
0xffff_feff to the hardware, which has a Write Only register behavior,
then we also want to have the mask cache be set to the same value for
consistency if nothing else. Am I failing at doing what I just described
and also failing at see it?
-- 
Florian