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SubjectRe: [PATCH 07/13] pci: Provide sensible irq vector alloc/free routines
On Mon, Jul 04, 2016 at 05:39:28PM +0900, Christoph Hellwig wrote:
> Add a function to allocate a range of interrupt vectors, which will
> transparently use MSI-X and MSI if available or fallback to legacy
> vectors. The interrupts are available in a core managed array in the
> pci_dev structure, and can also be released using a similar function.
> A new helper, __pci_enable_msix_range, is introduced to allow allocating
> the array of msix descriptors in the core PCIe code at the exact number
> of vectors supported by the PCI host complex, and to also help with the
> automatic IRQ affinity assignment that will be added in the next commit.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> Documentation/PCI/MSI-HOWTO.txt | 437 ++++------------------------------------

[...]

> + pci_enable_msi, pci_enable_msi_range, pci_enable_msi_exact, pci_disable_msi,
> + pci_msi_vec_count, pci_enable_msix_range, pci_enable_msix_exact,
> + pci_disable_msix, pci_msix_vec_count

Description of these functions can be removed when all drivers migrated
to the new API. Also implementation descriptions + examples would still
be needed AFAICT.

[...]

> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -4,6 +4,7 @@
> *
> * Copyright (C) 2003-2004 Intel
> * Copyright (C) Tom Long Nguyen (tom.l.nguyen@intel.com)
> + * Copyright (C) 2016 Christoph Hellwig.
> */
>
> #include <linux/err.h>
> @@ -1120,6 +1121,98 @@ int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
> }
> EXPORT_SYMBOL(pci_enable_msix_range);
>
> +static int __pci_enable_msix_range(struct pci_dev *dev, unsigned int min_vecs,
> + unsigned int max_vecs)
> +{
> + int vecs = max_vecs, ret, i;
> +
> +retry:
> + if (vecs < min_vecs)
> + return -ENOSPC;
> +
> + dev->msix_vectors = kmalloc_array(vecs, sizeof(struct msix_entry),
> + GFP_KERNEL);
> + if (!dev->msix_vectors)
> + return -ENOMEM;
> +
> + for (i = 0; i < vecs; i++)
> + dev->msix_vectors[i].entry = i;
> +
> + ret = pci_enable_msix(dev, dev->msix_vectors, vecs);
> + if (ret)
> + goto out_fail;
> +
> + return vecs;
> +
> +out_fail:
> + kfree(dev->msix_vectors);
> + dev->msix_vectors = NULL;
> +
> + if (ret >= 0) {
> + /* retry with the actually supported number of vectors */
> + vecs = ret;
> + goto retry;
> + }
> +
> + return ret;
> +}

This function's code almost matches the existing pci_enable_msix_range()
so pci_enable_msix_range() should be reworked instead IMHO.

I took a look at the existing code and the rework does not appear
necessary as __pci_enable_msix_range() could look like this:

static int __pci_enable_msix_range(struct pci_dev *dev, unsigned int min_vecs,
unsigned int max_vecs)
{
int ret, i;
struct msix_entry *entries;

entries = kmalloc_array(max_vecs, sizeof(entries[0]), GFP_KERNEL);
if (!entries)
return -ENOMEM;

for (i = 0; i < max_vecs; i++)
entries[i].entry = i;

ret = pci_enable_msix_range(dev, entries, min_vecs, max_vecs);

kfree(entries);

return ret;
}


We do not need to keep msix_entry array, since it only needed for
pci_irq_vector() function. But the same info could be retrieved from
msi_desc::irq.

> +/**
> + * pci_alloc_irq_vectors - allocate multiple IRQs for a device
> + * @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
> + *
> + * Allocate up to @max_vecs interrupt vectors for @dev, using MSI-X or MSI
> + * vectors if available, and fall back to a single legacy vector
> + * if neither is available. 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.
> + *
> + * To get the Linux irq number used for a vector that can be passed to
> + * request_irq use the pci_irq_vector() helper.
> + */
> +int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> + unsigned int max_vecs, unsigned int flags)
> +{
> + int vecs;
> +
> + if (!(flags & PCI_IRQ_NOMSIX)) {
> + vecs = __pci_enable_msix_range(dev, min_vecs, max_vecs);
> + if (vecs > 0)
> + return vecs;
> + }
> +
> + if (!(flags & PCI_IRQ_NOMSI)) {
> + vecs = pci_enable_msi_range(dev, min_vecs, max_vecs);
> + if (vecs > 0)
> + return vecs;
> + }
> +
> + /* use legacy irq if allowed */
> + if (min_vecs == 1)
> + return 1;
> + return -ENOSPC;

The original error code (in vecs) would be overridden with -ENOSPC here.

> +}
> +EXPORT_SYMBOL(pci_alloc_irq_vectors);
> +
> +/**
> + * pci_free_irq_vectors - free previously allocated IRQs for a device
> + * @dev: PCI device to operate on
> + *
> + * Undoes the allocations and enabling in pci_alloc_irq_vectors().
> + */
> +void pci_free_irq_vectors(struct pci_dev *dev)
> +{
> + if (dev->msix_enabled)
> + kfree(dev->msix_vectors);
> + pci_disable_msix(dev);
> + pci_disable_msi(dev);
> +}
> +EXPORT_SYMBOL(pci_free_irq_vectors);
> +
> struct pci_dev *msi_desc_to_pci_dev(struct msi_desc *desc)
> {
> return to_pci_dev(desc->dev);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index b67e4df..129871f 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -320,6 +320,7 @@ struct pci_dev {
> * directly, use the values stored here. They might be different!
> */
> unsigned int irq;
> + struct msix_entry *msix_vectors;

As suggested above, it is not needed.

> struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */
>
> bool match_driver; /* Skip attaching driver */
> @@ -1237,6 +1238,9 @@ resource_size_t pcibios_iov_resource_alignment(struct pci_dev *dev, int resno);
> int pci_set_vga_state(struct pci_dev *pdev, bool decode,
> unsigned int command_bits, u32 flags);
>
> +#define PCI_IRQ_NOMSI (1 << 0) /* don't try to use MSI interrupts */
> +#define PCI_IRQ_NOMSIX (1 << 1) /* don't try to use MSI-X interrupts */
> +
> /* kmem_cache style wrapper around pci_alloc_consistent() */
>
> #include <linux/pci-dma.h>
> @@ -1284,6 +1288,24 @@ static inline int pci_enable_msix_exact(struct pci_dev *dev,
> return rc;
> return 0;
> }
> +int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> + unsigned int max_vecs, unsigned int flags);
> +void pci_free_irq_vectors(struct pci_dev *dev);
> +
> +
> +/**
> + * pci_irq_vector - return Linux IRQ number of a device vector
> + * @dev: PCI device to operate on
> + * @nr: device-relative interrupt vector index (0-based).
> + */
> +static inline unsigned int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
> +{
> + if (dev->msix_enabled)
> + return dev->msix_vectors[nr].vector;

So here you could search with for_each_pci_msi_entry() instead.


> + WARN_ON_ONCE(!dev->msi_enabled && nr > 0);
> + return dev->irq + nr;

I think this function should check irq number existence and return the
vector number or -EINVAL;

> +}
> #else
> static inline int pci_msi_vec_count(struct pci_dev *dev) { return -ENOSYS; }
> static inline void pci_msi_shutdown(struct pci_dev *dev) { }
> @@ -1307,6 +1329,23 @@ static inline int pci_enable_msix_range(struct pci_dev *dev,
> static inline int pci_enable_msix_exact(struct pci_dev *dev,
> struct msix_entry *entries, int nvec)
> { return -ENOSYS; }
> +static inline int pci_alloc_irq_vectors(struct pci_dev *dev,
> + unsigned int min_vecs, unsigned int max_vecs,
> + unsigned int flags)
> +{
> + if (min_vecs > 1)
> + return -ENOSPC;

In case CONFIG_PCI_MSI is unset min_vecs > 1 is -EINVAL;

> + return 1;
> +}
> +static inline void pci_free_irq_vectors(struct pci_dev *dev)
> +{
> +}
> +
> +static inline unsigned int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
> +{
> + WARN_ON_ONCE(nr > 0);

As suggested above, it would rather -EINVAL;

> + return dev->irq;
> +}
> #endif
>
> #ifdef CONFIG_PCIEPORTBUS
> --
> 2.1.4
>

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