Date:   Mon, 5 Nov 2018 13:38:42 +0530
From:   Lokesh Vutla <lokeshvutla@...com>
To:     Marc Zyngier <marc.zyngier@....com>
CC:     Nishanth Menon <nm@...com>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        <jason@...edaemon.net>, Tero Kristo <t-kristo@...com>,
        Sekhar Nori <nsekhar@...com>, <linux-kernel@...r.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>, <tglx@...utronix.de>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 09/10] irqchip: ti-sci-inta: Add support for Interrupt
 Aggregator driver

Hi Marc,

On Monday 29 October 2018 06:34 PM, Lokesh Vutla wrote:
> Hi Marc,
> 
> On Sunday 28 October 2018 07:01 PM, Marc Zyngier wrote:
>> Hi Lokesh,
>>
>> On Fri, 26 Oct 2018 21:19:41 +0100,
>> Lokesh Vutla <lokeshvutla@...com> wrote:
>>>
>>> Hi Marc,
>>>
>>> [..snip..]
>>>>> [...]
>>>>>
>>>>>>>> +/**
>>>>>>>> + * ti_sci_inta_register_event() - Register a event to an interrupt aggregator
>>>>>>>> + * @dev:	Device pointer to source generating the event
>>>>>>>> + * @src_id:	TISCI device ID of the event source
>>>>>>>> + * @src_index:	Event source index within the device.
>>>>>>>> + * @virq:	Linux Virtual IRQ number
>>>>>>>> + * @flags:	Corresponding IRQ flags
>>>>>>>> + * @ack_needed:	If explicit clearing of event is required.
>>>>>>>> + *
>>>>>>>> + * Creates a new irq and attaches to IA domain if virq is not specified
>>>>>>>> + * else attaches the event to vint corresponding to virq.
>>>>>>>> + * When using TISCI within the client drivers, source indexes are always
>>>>>>>> + * generated dynamically and cannot be represented in DT. So client
>>>>>>>> + * drivers should call this API instead of platform_get_irq().
>>>>>>>
>>>>>>> NAK. Either this fits in the standard model, or we adapt the standard
>>>>>>> model to catter for your particular use case. But we don't define a new,
>>>>>>> TI specific API.
>>>>>>>
>>>>>>> I have a hunch that if the IDs are generated dynamically, then the model
>>>>>>> we use for MSIs would fit this thing. I also want to understand what
>>>>>>
>>>>>> hmm..I haven't thought about using MSI. Will try to explore it. But
>>>>>> the "struct msi_msg" is not applicable in this case as device does not
>>>>>> write to a specific location.
>>>>>
>>>>> It doesn't need to. You can perfectly ignore the address field and
>>>>> only be concerned with the data. We already have MSI users that do not
>>>>> need programming of the doorbell address, just the data.
>>>>
>>>
>>> Just one more clarification.
>>>
>>> First let me explain the IRQ routes a bit deeply. As I said earlier
>>> there are three ways in which IRQ can flow in AM65x SoC
>>> 1) Device directly connected to GIC
>>> 	- Device IRQ --> GIC
>>> 2) Device connected to INTR.
>>> 	- Device IRQ --> INTR --> GIC
>>> 3) Devices connected to INTA.
>>> 	- Device IRQ --> INTA --> INTR --> GIC
>>>
>>> 1 and 2 are straight forward and we use DT for IRQ
>>> representation. Coming to 3 the trickier part is that Input to INTA
>>> and output from INTA and dynamically managed. To be more specific:
>>> - By hardware design there are certain set of physical global
>>> events(interrupts) attached to an INTA. Out of which a certain range
>>> are assigned to the current linux host that can be queried from
>>> system-controller.
>>> - Similarly out of all the INTA outputs(referenced as vints) a certain
>>> range can be used by the current linux host.
>>>
>>>
>>> So for configuring an IRQ route in case 3, the following steps are needed:
>>> - Device id and device resource index for which the interrupt is needed
>>
>> THat is no different from a PCI device for example, where we need the
>> requester ID and the number of the interrupt in the MSI-X table.
>>
>>> - A free event id from the range assigned to the INTA in this host context
>>> - A free vint from the range assigned to the INTA in this host context
>>> - A free gic IRQ from the range assigned to the INTR in this host context.
>>
>>   From what I understand of the driver, at least some of that is under
>> the responsibility of the firmware, right? Or is the driver under
>> control of all three parameters? To be honest, it doesn't really
> 
> Driver should control all three parameters.
> 
>> matter, as the as far as the kernel is concerned, the irqchip drivers
>> are free to deal with the routing anyway they want.
> 
> Correct, that's my understanding as well.
> 
>>
>>> With the above information, linux should send a message to
>>> system-controller using TISCI protocol. After policing the given
>>> information, system-controller does the following:
>>> - Attaches the interrupt(INTA input) to the device resource index
>>> - Muxes the interrupt(INTA input) to corresponding vint(INTA output)
>>> - Muxes the vint(INTR input) to GIC irq(INTR output).
>>
>> Isn't there a 1:1 mapping between *used* INTR inputs and outputs?
>> Since INTR is a router, there is no real muxing. I assume that the
>> third point above is just a copy-paste error.
> 
> Right, my bad. INTR is just a router and no read muxing.
> 
>>
>>>
>>> For grouping of interrupts, the same vint number is to be passed to
>>> system-controller for all the requests.
>>>
>>> Keeping all the above in mind, I see the following as software IRQ
>>> Domain Hierarchy:
>>>
>>> 1) INTA multi MSI --> 2)INTA  -->3) MSI --> 4) INTR  -->5) GIC
>>>
>>> INTA driver has to set a chained IRQ using virq allocated from its
>>> parent MSI. This is to differentiate the grouped interrupts within
>>> INTA.
>>>
>>> Inorder to cover the above two MSI domains, a new bus driver has to be
>>> created as I couldn't find a fit with the existing bus drivers.
>>>
>>> Does the above approach make sense? Please correct me if i am wrong.
>>
>> I think this can be further simplified, as you seem to assume that
>> dynamic allocation implies MSI. This is not the case. You can
>> perfectly use dynamically allocated interrupts and still not use MSIs.
>>
>> INTA is indeed a chained interrupt controller, as it may mux several
>> inputs onto a single output. But the output of INTA is not an MSI. It
>> is just a regular interrupt that can allocated when the first mapping
>> gets established.
> 
> okay. I guess it can just be done using irq_create_fwspec_mapping().
> 

I am facing an issue with this approach as I am trying to call 
irq_create_fwspec_mapping() from alloc callback of INTA driver. During 
allocation the function call flow looks like:

inta_msi_domain_alloc_irqs()
	msi_domain_alloc_irqs()
		__irq_domain_alloc_irqs()
			*mutex_lock(&irq_domain_mutex);*
			irq_domain_alloc_irqs_hierarchy()
				ti_sci_inta_irq_domain_alloc()
					if (first event in group)
							irq_create_fwspec_mapping()
								irq_find_matching_fwspec()
									*mutex_lock(&irq_domain_mutex);*
									

The mutex_lock is called again if INTR IRQ gets allocated in alloc callback of 
INTA driver. So I am clearly calling irq_create_fwspec_mapping() from a wrong place.

To avoid this problem, some other msi domain ops should be used to allocate INTR 
irq. I see msi_prepare() might be a good place to allocate parent interrupt for 
each group. But there is no similar callback available while freeing. Is it okay 
to add msi_unprepare callback?

Also I would like to get the parent(INTR) IRQ to get established first as we 
need the gic_irq, vint_id while configuring the IRQ route using system-controller.

Any help on avoiding this problem?

Thanks and regards,
Lokesh

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