From: Rahul Singh <Rahul.Singh@arm.com> To: Jan Beulich <email@example.com> Cc: "Julien Grall" <firstname.lastname@example.org>, xen-devel <email@example.com>, "Bertrand Marquis" <Bertrand.Marquis@arm.com>, "Paul Durrant" <firstname.lastname@example.org>, "Andrew Cooper" <email@example.com>, "George Dunlap" <firstname.lastname@example.org>, "Ian Jackson" <email@example.com>, "Stefano Stabellini" <firstname.lastname@example.org>, "Wei Liu" <email@example.com>, "Daniel De Graaf" <firstname.lastname@example.org>, "Roger Pau Monné" <email@example.com> Subject: Re: [PATCH 2/2] xen/pci: Gate all MSI code in common code with CONFIG_HAS_PCI_MSI Date: Thu, 8 Apr 2021 08:45:06 +0000 [thread overview] Message-ID: <479D17E5-3021-4A2E-B066-D179226CC48B@arm.com> (raw) In-Reply-To: <firstname.lastname@example.org> Hi, > On 8 Apr 2021, at 7:00 am, Jan Beulich <email@example.com> wrote: > > On 07.04.2021 20:06, Julien Grall wrote: >> Hi Jan, >> >> On 06/04/2021 16:25, Jan Beulich wrote: >>> On 06.04.2021 16:30, Julien Grall wrote: >>>> Hi Roger, >>>> >>>> On 06/04/2021 15:13, Roger Pau Monné wrote: >>>>> On Tue, Apr 06, 2021 at 12:39:11PM +0100, Rahul Singh wrote: >>>>>> MSI support is not implemented for ARM architecture but it is enabled >>>>>> for x86 architecture and referenced in common passthrough/pci.c code. >>>>>> >>>>>> Therefore introducing the new flag to gate the MSI code for ARM in >>>>>> common code to avoid compilation error when HAS_PCI is enabled for ARM. >>>>> >>>>> Is such option really interesting long term? >>>>> >>>>> IIRC PCI Express mandates MSI support, at which point I don't see much >>>>> value in being able to compile out the MSI support. >>>> >>>> I am pretty sure there are board out with PCI support but no MSI >>>> support. Anyway, even if the spec may mandate it... >>>> >>>>> >>>>> So while maybe helpful for Arm PCI efforts ATM, I'm not sure it >>>>> warrants a Kconfig option, I would rather see Arm introduce dummy >>>>> helpers for the missing functionality, even if unimplemented at the >>>>> moment. >>>> >>>> ... from my understanding, most of (if not all) the MSI code is not very >>>> useful on Arm when using the GICv3 ITS. >>>> >>>> The GICv3 ITS will do the isolation for you and therefore we should not >>>> need to keep track of the state at the vPCI level. >>> >>> But that's then not "has PCI MSI" but "need to intercept PCI MSI >>> accesses", i.e. I don't think the Kconfig option is correctly >>> named. If a device with MSI support is used, you can't make that >>> MSI support go away, after all. >> >> That's actually a good point. Rahul, do you think the config can be >> renamed to something like CONFIG_PCI_MSI_NEED_INTERCEPT? > > Minor remark: In this name I'd be inclined to suggest to omit NEED. > OK . I will use the name CONFIG_PCI_MSI_INTERCEPT and will send next version of the patch. Regards, Rahul > Jan
prev parent reply other threads:[~2021-04-08 8:46 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-06 11:39 [PATCH 0/2] xen/pci: Make PCI passthrough code non-x86 specific Rahul Singh 2021-04-06 11:39 ` [PATCH 1/2] xen/pci: Move PCI ATS code to common directory Rahul Singh 2021-04-06 15:16 ` Jan Beulich 2021-04-06 11:39 ` [PATCH 2/2] xen/pci: Gate all MSI code in common code with CONFIG_HAS_PCI_MSI Rahul Singh 2021-04-06 14:13 ` Roger Pau Monné 2021-04-06 14:30 ` Julien Grall 2021-04-06 14:59 ` Roger Pau Monné 2021-04-06 15:09 ` Julien Grall 2021-04-06 15:58 ` Roger Pau Monné 2021-04-07 17:52 ` Rahul Singh 2021-04-06 15:25 ` Jan Beulich 2021-04-07 18:06 ` Julien Grall 2021-04-08 6:00 ` Jan Beulich 2021-04-08 8:45 ` Rahul Singh [this message]
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