Re: [PATCH V7 2/3] ACPI: Add support for ResourceSource/IRQ domain mapping

[Agustin Vega-Frias]

Hi Lorenzo,

On 2016-11-29 07:11, Lorenzo Pieralisi wrote:
> Hi Agustin,
>
> On Mon, Nov 28, 2016 at 05:40:24PM -0500, Agustin Vega-Frias wrote:
> > Hi Rafael,
> >
> > Can you chime in on Lorenzo's feedback and the discussion below?
> > It would be great if you can comment on the reason ACPI does things
> > in a certain way.
> >
> > Hi Lorenzo,
> >
> > On 2016-11-25 06:40, Lorenzo Pieralisi wrote:
> > >Hi Agustin,
> > >
> > >On Thu, Nov 24, 2016 at 04:15:48PM +0000, Lorenzo Pieralisi wrote:
> > >
> > >[...]
> > >
> > >>> @@ -448,6 +449,7 @@ bool acpi_dev_resource_interrupt(struct acpi_resource *ares, int index,
> > >>>  {
> > >>>  	struct acpi_resource_irq *irq;
> > >>>  	struct acpi_resource_extended_irq *ext_irq;
> > >>> +	struct fwnode_handle *src;
> > >>>
> > >>>  	switch (ares->type) {
> > >>>  	case ACPI_RESOURCE_TYPE_IRQ:
> > >>> @@ -460,7 +462,7 @@ bool acpi_dev_resource_interrupt(struct acpi_resource *ares, int index,
> > >>>  			acpi_dev_irqresource_disabled(res, 0);
> > >>>  			return false;
> > >>>  		}
> > >>> -		acpi_dev_get_irqresource(res, irq->interrupts[index],
> > >>> +		acpi_dev_get_irqresource(res, irq->interrupts[index], NULL,
> > >>>  					 irq->triggering, irq->polarity,
> > >>>  					 irq->sharable, true);
> > >>>  		break;
> > >>> @@ -470,7 +472,8 @@ bool acpi_dev_resource_interrupt(struct acpi_resource *ares, int index,
> > >>>  			acpi_dev_irqresource_disabled(res, 0);
> > >>>  			return false;
> > >>>  		}
> > >>> -		acpi_dev_get_irqresource(res, ext_irq->interrupts[index],
> > >>> +		src = acpi_get_irq_source_fwhandle(&ext_irq->resource_source);
> > >>
> > >>Is there a reason why we need to do the domain look-up here ?
> >
> > Because we need to pass the resource down to acpi_dev_get_irqresource
> > which does the mapping through acpi_register_irq/acpi_register_gsi.
> >
> > >>
> > >>I would like to understand if, by reshuffling the code (and by
> > >>returning
> > >>the resource_source to the calling code - somehow), it would be
> > >>possible
> > >>to just mirror what the OF code does in of_irq_get(), namely:
> > >>
> > >>(1) parse the irq entry -> of_irq_parse_one()
> > >>(2) look the domain up -> irq_find_host()
> > >>(3) create the mapping -> irq_create_of_mapping()
> > >>
> > >>You wrote the code already, I think it is just a matter of shuffling
> > >>it around (well, minus returning the resource_source to the caller
> > >>which is phandle equivalent in DT).
> >
> > This is one area in which DT and ACPI are fundamentally different. In 
> > DT
> > once the flattened blob is expanded the data is fixed. In ACPI the 
> > data
> > returned by a method can change. In reality most methods like CRS 
> > return
> > constants, but given that per-spec they are methods the interpreter 
> > has
> > to be involved, which makes it an expensive operation. I believe that 
> > is
> > the reason the resource parsing code in ACPI attempts all mappings
> > during
> > the bus scan. Rafael can you comment on this?
> >
> > One way to do what you suggest would be to defer IRQ mapping by, e.g.,
> > populating res->start with the HW IRQ number and res->end with the
> > fwnode.
> > That way we can avoid having to walk the resource buffer when a 
> > mapping
> > is needed. I don't think that approach would deviate much more from
> > the spec from what the current ahead-of-time mapping does, but it 
> > would
> > require more changes in the core code. An alternative would be to do
> > that only for resources that fail to map.
> >
> > >>
> > >>You abstracted away (2) and (3) behind acpi_register_irq(), that
> > >>on anything than does not use ACPI_GENERIC_GSI is just glue code
> > >>to acpi_register_gsi().
> > >>
> > >>Also, it is not a question on this patch but I ask it here because it
> > >>is related. On ACPI you are doing the reverse of what is done in
> > >>DT in platform_get_irq():
> > >>
> > >>- get the resources already parsed -> platform_get_resource()
> > >>- if they are disabled -> acpi_irq_get()
> > >>
> > >>and I think the ordering is tied to my question above because
> > >>you carry out the domain look up in acpi_dev_resource_interrupt()
> > >>so that if for any reason it fails the corresponding resource
> > >>is disabled so that we try to get it again through acpi_irq_get().
> > >>
> > >>I suspect you did it this way to make sure:
> > >>
> > >>a) keep the current ACPI IRQ parsing interface changes to a mininum
> > >>b) avoid changing the behaviour on x86/ia64; in particular, calling
> > >>   acpi_register_gsi() for the _same_ mapping (an IRQ that was already
> > >>   registered at device creation resource parsing) multiple times can
> > >>   trigger issues on x86/ia64
> >
> > You are correct about my reasons. I wanted to keep ACPI core code
> > changes
> > to a minimum, and I also needed to work within the current
> > implementation
> > which uses the pre-converted IRQ resources.
> >
> > >>
> > >>I think that's a reasonable approach but I wanted to get these
> > >>clarifications, I do not think you are far from getting this
> > >>done but since it is a significant change I think it is worth
> > >>discussing the points I raised above because I think the DT code
> > >>sequence in of_irq_get() (1-2-3 above) is cleaner from an IRQ
> > >>layer perspective (instead of having the domain look-up buried
> > >>inside the ACPI IRQ resource parsing API).
> > >
> > >I had another look and to achieve the above one way of doing that is to
> > >implement acpi_irq_get() only for ACPI_GENERIC_GSI and stub it out for
> > >!ACPI_GENERIC_GSI (ie return an error code so that on !ACPI_GENERIC_GSI
> > >we would fall back to current solution for ACPI). Within acpi_irq_get()
> > >you can easily carry out the same steps (1->2->3) above in ACPI
> > >you have
> > >the code already there I think it is easy to change the
> > >acpi_irq_get_cb() interface to return a filled in struct irq_fwspec and
> > >the interface would become identical to of_irq_get() that is an
> > >advantage to maintain it from an IRQ maintainership perspective I
> > >think,
> > >that's my opinion.
> >
> > I think I get what you mean. I'll take a stab at implementing
> > acpi_irq_get()
> > in the way you suggest.
> >
> > >
> > >There is still a nagging snag though. When platform devices are
> > >created, core ACPI code parse the resources through:
> > >
> > >acpi_dev_get_resources()
> > >
> > >and we _have_ to have way to avoid initializing IRQ resources that
> > >have a dependency (ie there is a resource_source pointer that is valid
> > >in their descriptors) that's easy to do if we think that's the right
> > >thing to do and can hardly break current code (which ignores the
> > >resource_source altogether).
> >
> > I'd rather keep the core code as-is with regard to the ahead-of-time
> > conversion. Whether a resource source is available at the time of
> > the bus
> > scan should be transparent to the code in drivers/acpi/resource.c, and
> > we need the initialization as a disabled resource to signal the need
> > to retry anyway.
>
> Yes, exactly that's the nub. Your current code works, I am trying to
> make it more modular and similar to the DT/irqdomain IRQ look-up path,
> which has its advantages.
>
> There are two options IMHO:
>
> - always disable the resource if it has a resource_source dependency 
> and defer
>   its parsing to acpi_irq_get() (where you can easily implement steps
> 1-2-3 above).
>   What I wanted to say is that, by disabling the resource if it has a
>   resource_source dependency you can't break x86/ia64 (it is ignored at
>   present - hopefully there is nothing that we are not aware of behind
>   that choice). On x86/ia64 acpi_irq_get() would be an empty stub.
>   This way you would keep the irqdomain look-up out of the ACPI 
> resource
>   parsing API, correct ?
> - keep code as-is

I plan to work on V8 today to address the point you raised w.r.t. making
it look more like DT for maintainability. I will leave other things 
as-is
with an understanding that we might revisit based on Rafael's feedback

Thanks,
Agustin

> Your point on _CRS being _current_ resource setting is perfectly valid
> so platform_get_resource() in platform_get_irq() must always take
> precedence over acpi_irq_get() (which should just apply to disabled
> resources), I am not sure that doing it the other way around is safe.
>
> > Rafael, do you have any other suggestions/feedback on how to go about
> > doing this?
>
> Yes, comments very appreciated, these changes are not trivial and need
> agreement.
>
> Thanks,
> Lorenzo
>
> > Thanks,
> > Agustin
> >
> > >
> > >It is an important difference with DT probing, where the IRQ
> > >resources are only created if the domain reference (ie interrupt
> > >controller phandle) is satisfied at of_device_alloc() time
> > >(see of_device_alloc()).
> > >
> > >Thoughts ? Please let me know, the code to implement what I say
> > >is already in these patches, it is just a matter of reshuffling it.
> > >
> > >Thanks !
> > >Lorenzo
> >
> > --
> > Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm
> > Technologies, Inc.
> > Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a
> > Linux Foundation Collaborative Project.

--
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a 
Linux Foundation Collaborative Project.