Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754794AbcK2Q0g (ORCPT ); Tue, 29 Nov 2016 11:26:36 -0500 Received: from mail-wj0-f194.google.com ([209.85.210.194]:33457 "EHLO mail-wj0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754123AbcK2Q01 (ORCPT ); Tue, 29 Nov 2016 11:26:27 -0500 MIME-Version: 1.0 In-Reply-To: References: <1479074375-2629-1-git-send-email-agustinv@codeaurora.org> <1479074375-2629-3-git-send-email-agustinv@codeaurora.org> <20161124161548.GA11766@red-moon> <20161125114035.GA13739@red-moon> <20161129121152.GA32453@red-moon> From: "Rafael J. Wysocki" Date: Tue, 29 Nov 2016 17:26:25 +0100 X-Google-Sender-Auth: hrYwOCKwn63i2CbeszR_ybDMzgA Message-ID: Subject: Re: [PATCH V7 2/3] ACPI: Add support for ResourceSource/IRQ domain mapping To: Agustin Vega-Frias Cc: "Rafael J. Wysocki" , Lorenzo Pieralisi , Linux Kernel Mailing List , ACPI Devel Maling List , "linux-arm-kernel@lists.infradead.org" , "Rafael J. Wysocki" , Len Brown , Thomas Gleixner , Jason Cooper , Marc Zyngier , Timur Tabi , Christopher Covington , Andy Gross , harba@codeaurora.org, Jon Masters , Mark Salter , Mark Langsdorf , Al Stone , astone@redhat.com, Graeme Gregory , Hanjun Guo , Charles Garcia Tobin Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9550 Lines: 225 On Tue, Nov 29, 2016 at 4:20 PM, Agustin Vega-Frias wrote: > Hi Rafael, > > > On 2016-11-29 07:43, Rafael J. Wysocki wrote: >> >> On Tue, Nov 29, 2016 at 1:11 PM, 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 >>> >>> 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. >> >> >> So I need more time. > > > Please wait for V8 which will address some issues raised by Lorenzo. > >> >> But basically, _CRS can't really change on the fly AFAICS. I'm not >> even sure it is valid for it to change at all after the first >> evaluation if _SRS/_PRS are not present. > > > That's good to know and it opens more possibilities. Actually, to me it follows from the very purpose of _CRS that, as long as the device is enabled, it should be expected to return the same data every time it is evaluated, unless _SRS is invoked in the meantime. Otherwise, it would be possible for the device's resources to change unexpectedly under a driver using it. Thanks, Rafael