linux-kernel - Re: [PATCH v7 1/4] PCI: Introduce pcim_alloc_irq

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Message-ID: <20210610224143.GA2785655@bjorn-Precision-5520>
Date:   Thu, 10 Jun 2021 17:41:43 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Dejin Zheng <zhengdejin5@...il.com>
Cc:     corbet@....net, jarkko.nikula@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        rric@...nel.org, bhelgaas@...gle.com, wsa@...nel.org,
        Sanket.Goswami@....com, linux-doc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v7 1/4] PCI: Introduce pcim_alloc_irq_vectors()

On Mon, Jun 07, 2021 at 11:39:13PM +0800, Dejin Zheng wrote:
> Introduce pcim_alloc_irq_vectors(), a device-managed version of
> pci_alloc_irq_vectors(). Introducing this function can simplify
> the error handling path in many drivers.
> 
> And use pci_free_irq_vectors() to replace some code in pcim_release(),
> they are equivalent, and no functional change. It is more explicit
> that pcim_alloc_irq_vectors() is a device-managed function.

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 452351025a09..e3b3fc59bd35 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1989,10 +1989,7 @@ static void pcim_release(struct device *gendev, void *res)
>  	struct pci_devres *this = res;
>  	int i;
>  
> -	if (dev->msi_enabled)
> -		pci_disable_msi(dev);
> -	if (dev->msix_enabled)
> -		pci_disable_msix(dev);
> +	pci_free_irq_vectors(dev);

If I understand correctly, this hunk is a nice simplification, but
actually has nothing to do with making pcim_alloc_irq_vectors().  I
have it split to a separate patch in my local tree.  Or am I wrong
about that?

>  	for (i = 0; i < DEVICE_COUNT_RESOURCE; i++)
>  		if (this->region_mask & (1 << i))
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index c20211e59a57..5783262c4643 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1730,6 +1730,7 @@ static inline struct pci_dev *pci_get_class(unsigned int class,
>  
>  static inline void pci_set_master(struct pci_dev *dev) { }
>  static inline int pci_enable_device(struct pci_dev *dev) { return -EIO; }
> +static inline int pci_is_managed(struct pci_dev *pdev) { return 0; }
>  static inline void pci_disable_device(struct pci_dev *dev) { }
>  static inline int pcim_enable_device(struct pci_dev *pdev) { return -EIO; }
>  static inline int pci_assign_resource(struct pci_dev *dev, int i)
> @@ -1825,6 +1826,30 @@ pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>  					      NULL);
>  }
>  
> +/**
> + * pcim_alloc_irq_vectors - a device-managed pci_alloc_irq_vectors()
> + * @dev:		PCI device to operate on
> + * @min_vecs:		minimum number of vectors required (must be >= 1)
> + * @max_vecs:		maximum (desired) number of vectors
> + * @flags:		flags or quirks for the allocation
> + *
> + * Return the number of vectors allocated, (which might be smaller than
> + * @max_vecs) if successful, or a negative error code on error. If less
> + * than @min_vecs interrupt vectors are available for @dev the function
> + * will fail with -ENOSPC.
> + *
> + * It depends on calling pcim_enable_device() to make IRQ resources
> + * manageable.
> + */
> +static inline int
> +pcim_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> +			unsigned int max_vecs, unsigned int flags)
> +{
> +	if (!pci_is_managed(dev))
> +		return -EINVAL;
> +	return pci_alloc_irq_vectors(dev, min_vecs, max_vecs, flags);

This is great, but can you explain how pci_alloc_irq_vectors()
magically becomes a managed interface if we've already called
pcim_enable_device()?

I certainly believe it does; I'd just like to put a hint in the commit
log since my 5 minutes of grepping around didn't make it obvious to
me.

I see that pcim_enable_device() sets pdev->is_managed, but I didn't
find the connection between that and pci_alloc_irq_vectors().

> +}
> +
>  /* Include architecture-dependent settings and functions */
>  
>  #include <asm/pci.h>
> -- 
> 2.30.1
>