linux-kernel - RE: [patch V2 07/33] genirq/msi: Provide msi_create/free_device_irq

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Date:   Thu, 24 Nov 2022 01:07:07 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     "x86@...nel.org" <x86@...nel.org>, Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        "linux-pci@...r.kernel.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>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>
Subject: RE: [patch V2 07/33] genirq/msi: Provide
 msi_create/free_device_irq_domain()

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Wednesday, November 23, 2022 7:38 PM
> 
> >> + *
> >> + * Return: True on success, false otherwise
> >
> > Can you elaborate why boolean type is selected instead of returning the
> > actual error codes? the outmost callers are all new functions:
> >
> > 	pci_setup_msi[x]_device_domain()
> > 	pci_create_ims_domain()
> >
> > I didn't find out any legacy convention forcing this way...
> 
> What's the value of error codes? 99% of all callsites do:
> 
>        ret = foo();
>        if (ret)
>           goto fail;
> 
> Nothing evaluates the error codes, unless there is real useful
> information like EAGAIN or ENOSPC which can tell the caller to retry
> eventually or with different parameters. But for the above, the error
> code is just useless.
> 

I looked at it from the outmost invocation:

@@ -436,6 +436,9 @@ int __pci_enable_msi_range(struct pci_de
 	if (rc)
 		return rc;
 
+	if (!pci_setup_msi_device_domain(dev))
+		return -ENODEV;
+

the current style kind of converts meaningful -EINVAL/-ENOMEM/etc.
into -ENODEV.