linux-kernel - Re: [PATCH v2 1/2] PCI/MSI: Fix the confusing IRQ sysfs ABI for MSI-X

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Date:   Mon, 23 Aug 2021 11:33:15 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>, Jonathan.Cameron@...wei.com,
        bilbao@...edu, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        leon@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org, Linuxarm <linuxarm@...wei.com>,
        luzmaximilian@...il.com, mchehab+huawei@...nel.org,
        schnelle@...ux.ibm.com, Barry Song <song.bao.hua@...ilicon.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/2] PCI/MSI: Fix the confusing IRQ sysfs ABI for MSI-X

On Sat, 21 Aug 2021 23:41:17 +0100,
Barry Song <21cnbao@...il.com> wrote:

[...]

> > So probably we should set this ABI invisible when devices are using
> > MSI or MSI-X?
> 
> i mean something like the below,
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 5d63df7..1323841 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -26,6 +26,7 @@
>  #include <linux/slab.h>
>  #include <linux/vgaarb.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/msi.h>
>  #include <linux/of.h>
>  #include "pci.h"
> 
> @@ -1437,6 +1438,16 @@ static umode_t pci_dev_attrs_are_visible(struct
> kobject *kobj,
>                 if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
>                         return 0;
> 
> +#ifdef CONFIG_PCI_MSI
> +       /*
> +        * if devices are MSI and MSI-X, IRQ sysfs ABI is meaningless
> +        * and broken
> +        */
> +       if (a == &dev_attr_irq.attr)
> +               if (first_pci_msi_entry(pdev))
> +                       return 0;
> +#endif
> +
>         return a->mode;
>  }

I don't think you can break what we have today. Whatever change we
make to the kernel internals, the userspace view must stay unchanged.

	M.

-- 
Without deviation from the norm, progress is not possible.