linux-kernel - Re: [PATCH v3 2/3] PCI/sysfs: Don't depend on pci

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Date:   Wed, 25 Aug 2021 14:30:04 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     bhelgaas@...gle.com, tglx@...utronix.de,
        Jonathan.Cameron@...wei.com, bilbao@...edu, corbet@....net,
        gregkh@...uxfoundation.org, leon@...nel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linuxarm@...wei.com, luzmaximilian@...il.com,
        mchehab+huawei@...nel.org, schnelle@...ux.ibm.com,
        jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        intel-wired-lan@...ts.osuosl.org,
        Barry Song <song.bao.hua@...ilicon.com>
Subject: Re: [PATCH v3 2/3] PCI/sysfs: Don't depend on pci_dev.irq for IRQ entry

On Wed, 25 Aug 2021 11:26:35 +0100,
Barry Song <21cnbao@...il.com> wrote:
> 
> From: Barry Song <song.bao.hua@...ilicon.com>
> 
> Explicitly use IRQ number from MSI list for IRQ sysfs entry. Then sysfs
> will decouple with the odd implementation depending on pci_dev.irq.
> 
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> ---
>  drivers/pci/pci-sysfs.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 7bbf2673..f5a06b9 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"
>  
> @@ -49,7 +50,27 @@ static DEVICE_ATTR_RO(field)
>  pci_config_attr(subsystem_device, "0x%04x\n");
>  pci_config_attr(revision, "0x%02x\n");
>  pci_config_attr(class, "0x%06x\n");
> -pci_config_attr(irq, "%u\n");
> +
> +static ssize_t irq_show(struct device *dev,
> +			struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +#ifdef CONFIG_PCI_MSI
> +	/*
> +	 * For MSI, return the 1st IRQ in IRQ vector; for all other cases
> +	 * including MSI-X, return legacy INTx
> +	 */
> +	if (pdev->msi_enabled) {
> +		struct msi_desc *desc = first_pci_msi_entry(pdev);
> +
> +		return sysfs_emit(buf, "%u\n", desc->irq);
> +	}
> +#endif

nit: It would be worth adding a comment indicating that we only do
this to preserve an existing userspace ABI. Just in case someone
thinks it is pointless and remove it... ;-)

	M.

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