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    SubjectRe: [PATCH v2 -tip 4/5] PCI, MSI: Enable multiple MSIs with pci_enable_msi_block_auto()
    On Mon, Sep 3, 2012 at 2:19 AM, Alexander Gordeev <agordeev@redhat.com> wrote:
    > The new function pci_enable_msi_block_auto() tries to allocate maximum
    > possible number of MSIs up to the number the device supports. It
    > generalizes a pattern when pci_enable_msi_block() is contiguously called
    > until it succeeds or fails.
    >
    > Opposite to pci_enable_msi_block() which takes the number of MSIs to
    > allocate as a input parameter, pci_enable_msi_block_auto() could be used
    > by device drivers to obtain the number of assigned MSIs and the number
    > of MSIs the device supports.
    >
    > Signed-off-by: Alexander Gordeev <agordeev@redhat.com>

    Acked-by: Bjorn Helgaas <bhelgaas@google.com>

    I haven't looked at the other patches in this series, but if the
    x86/IRQ folks like them, I'm OK with this part.

    Since the series is mostly non-PCI, I think it makes the most sense to
    keep it all together and merge it through some x86 or IRQ tree,
    including this PCI bit.

    > ---
    > Documentation/PCI/MSI-HOWTO.txt | 37 ++++++++++++++++++++++++++++++++-----
    > drivers/pci/msi.c | 26 ++++++++++++++++++++++++++
    > include/linux/pci.h | 7 +++++++
    > 3 files changed, 65 insertions(+), 5 deletions(-)
    >
    > diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
    > index 53e6fca..a091780 100644
    > --- a/Documentation/PCI/MSI-HOWTO.txt
    > +++ b/Documentation/PCI/MSI-HOWTO.txt
    > @@ -127,15 +127,42 @@ on the number of vectors that can be allocated; pci_enable_msi_block()
    > returns as soon as it finds any constraint that doesn't allow the
    > call to succeed.
    >
    > -4.2.3 pci_disable_msi
    > +4.2.3 pci_enable_msi_block_auto
    > +
    > +int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *count)
    > +
    > +This variation on pci_enable_msi() call allows a device driver to request
    > +the maximum possible number of MSIs. The MSI specification only allows
    > +interrupts to be allocated in powers of two, up to a maximum of 2^5 (32).
    > +
    > +If this function returns a positive number, it indicates that it has
    > +succeeded and the returned value is the number of allocated interrupts. In
    > +this case, the function enables MSI on this device and updates dev->irq to
    > +be the lowest of the new interrupts assigned to it. The other interrupts
    > +assigned to the device are in the range dev->irq to dev->irq + returned
    > +value - 1.
    > +
    > +If this function returns a negative number, it indicates an error and
    > +the driver should not attempt to request any more MSI interrupts for
    > +this device.
    > +
    > +If the device driver needs to know the number of interrupts the device
    > +supports it can pass the pointer count where that number is stored. The
    > +device driver must decide what action to take if pci_enable_msi_block_auto()
    > +succeeds, but returns a value less than the number of interrupts supported.
    > +If the device driver does not need to know the number of interrupts
    > +supported, it can set the pointer count to NULL.
    > +
    > +4.2.4 pci_disable_msi
    >
    > void pci_disable_msi(struct pci_dev *dev)
    >
    > This function should be used to undo the effect of pci_enable_msi() or
    > -pci_enable_msi_block(). Calling it restores dev->irq to the pin-based
    > -interrupt number and frees the previously allocated message signaled
    > -interrupt(s). The interrupt may subsequently be assigned to another
    > -device, so drivers should not cache the value of dev->irq.
    > +pci_enable_msi_block() or pci_enable_msi_block_auto(). Calling it restores
    > +dev->irq to the pin-based interrupt number and frees the previously
    > +allocated message signaled interrupt(s). The interrupt may subsequently be
    > +assigned to another device, so drivers should not cache the value of
    > +dev->irq.
    >
    > Before calling this function, a device driver must always call free_irq()
    > on any interrupt for which it previously called request_irq().
    > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
    > index f0752d1..690b268 100644
    > --- a/drivers/pci/msi.c
    > +++ b/drivers/pci/msi.c
    > @@ -845,6 +845,32 @@ int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
    > }
    > EXPORT_SYMBOL(pci_enable_msi_block);
    >
    > +int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec)
    > +{
    > + int ret, pos, nvec;
    > + u16 msgctl;
    > +
    > + pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
    > + if (!pos)
    > + return -EINVAL;
    > +
    > + pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &msgctl);
    > + ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
    > +
    > + if (maxvec)
    > + *maxvec = ret;
    > +
    > + do {
    > + nvec = ret;
    > + ret = pci_enable_msi_block(dev, nvec);
    > + } while (ret > 0);
    > +
    > + if (ret < 0)
    > + return ret;
    > + return nvec;
    > +}
    > +EXPORT_SYMBOL(pci_enable_msi_block_auto);
    > +
    > void pci_msi_shutdown(struct pci_dev *dev)
    > {
    > struct msi_desc *desc;
    > diff --git a/include/linux/pci.h b/include/linux/pci.h
    > index 5faa831..b8a9454 100644
    > --- a/include/linux/pci.h
    > +++ b/include/linux/pci.h
    > @@ -1070,6 +1070,12 @@ static inline int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
    > return -1;
    > }
    >
    > +static inline int
    > +pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec)
    > +{
    > + return -1;
    > +}
    > +
    > static inline void pci_msi_shutdown(struct pci_dev *dev)
    > { }
    > static inline void pci_disable_msi(struct pci_dev *dev)
    > @@ -1101,6 +1107,7 @@ static inline int pci_msi_enabled(void)
    > }
    > #else
    > extern int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec);
    > +extern int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec);
    > extern void pci_msi_shutdown(struct pci_dev *dev);
    > extern void pci_disable_msi(struct pci_dev *dev);
    > extern int pci_msix_table_size(struct pci_dev *dev);
    > --
    > 1.7.7.6
    >
    >
    > --
    > Regards,
    > Alexander Gordeev
    > agordeev@redhat.com


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