linux-kernel - Re: [patch V3 28/33] PCI/MSI: Provide IMS (Interrupt Message Store) support

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Message-ID: <20240327163247.GA1525799@bhelgaas>
Date: Wed, 27 Mar 2024 11:32:47 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Marc Zyngier <maz@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Gunthorpe <jgg@...lanox.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Ashok Raj <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
	Allen Hubbe <allenbh@...il.com>
Subject: Re: [patch V3 28/33] PCI/MSI: Provide IMS (Interrupt Message Store)
 support

On Fri, Nov 25, 2022 at 12:26:29AM +0100, Thomas Gleixner wrote:
> IMS (Interrupt Message Store) is a new specification which allows
> implementation specific storage of MSI messages contrary to the
> strict standard specified MSI and MSI-X message stores.
> ...

> + * pci_create_ims_domain - Create a secondary IMS domain for a PCI device

> + * Return: True on success, false otherwise

> +bool pci_create_ims_domain(struct pci_dev *pdev, const struct msi_domain_template *template,
> +			   unsigned int hwsize, void *data)

pci_create_ims_domain() is exported for use by modules, but AFAICT,
there is no in-tree user of this yet.

I assume one is coming, but if there isn't one on the near horizon,
we could/should remove this for now.

Either way, I think "bool" is not the optimal return type because
"pci_create_ims_domain" doesn't lend itself to a "true/false" reading
and most interfaces that actually do something return 0 for success or
a negative errno, so this will look like the opposite in the caller.

I have similar comments about the following interfaces returning
"bool", but they are internal to the PCI core:

  bool pci_create_device_domain()
  bool pci_setup_msi_device_domain()
  bool pci_setup_msix_device_domain()

Bjorn