Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933535AbcK2MoA (ORCPT ); Tue, 29 Nov 2016 07:44:00 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33232 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755684AbcK2Mnu (ORCPT ); Tue, 29 Nov 2016 07:43:50 -0500 MIME-Version: 1.0 In-Reply-To: <20161129121152.GA32453@red-moon> 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 13:43:48 +0100 X-Google-Sender-Auth: L2IkdME3Yyn7dgpgQwivbeHCAMU Message-ID: Subject: Re: [PATCH V7 2/3] ACPI: Add support for ResourceSource/IRQ domain mapping To: Lorenzo Pieralisi Cc: Agustin Vega-Frias , 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: 8482 Lines: 193 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. 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. Thanks, Rafael