Hi Alex,
pci_get_slot() will hold a reference count on the returned
pci device, so need to release the reference count for balance.
According to patches "[PATCH 5/7] amd_iommu: Make use of DMA quirks
and ACS checks in IOMMU groups" and "[PATCH 6/7] intel-iommu: Make
use of DMA quirks and ACS checks in IOMMU groups", current patches
failed to release the reference count gained by pci_get_slot().
Thanks
Gerry
On 05/30/2012 12:48 PM, Alex Williamson wrote:
> DMA transactions are tagged with the source ID of the device making
> the request. Occasionally hardware screws this up and uses the
> source ID of a different device (often the wrong function number of
> a multifunction device). A specific Ricoh multifunction device is
> a prime example of this problem and included in this patch. The
> purpose of this function is that given a pci_dev, return the pci_dev
> to use as the source ID for DMA. When hardware works correctly,
> this returns the input device. For the components of the Ricoh
> multifunction device, return the pci_dev for function 0.
>
> This will be used by IOMMU drivers for determining the boundaries
> of IOMMU groups as multiple devices using the same source ID must
> be contained within the same group. This can also be used by
> existing streaming DMA paths for the same purpose.
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>
> drivers/pci/quirks.c | 40 ++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 5 +++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 2a75216..004e167 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3179,3 +3179,43 @@ int pci_dev_specific_reset(struct pci_dev *dev, int probe)
>
> return -ENOTTY;
> }
> +
> +static struct pci_dev *pci_func_0_dma_source(struct pci_dev *dev)
> +{
> + return pci_get_slot(dev->bus, PCI_DEVFN(PCI_SLOT(dev->devfn), 0));
> +}
> +
> +static const struct pci_dev_dma_source {
> + u16 vendor;
> + u16 device;
> + struct pci_dev *(*dma_source)(struct pci_dev *dev);
> +} pci_dev_dma_source[] = {
> + /*
> + * https://bugzilla.redhat.com/show_bug.cgi?id=605888
> + *
> + * Some Ricoh devices use the function 0 source ID for DMA on
> + * other functions of a multifunction device. The DMA devices
> + * is therefore function 0, which will have implications of the
> + * iommu grouping of these devices.
> + */
> + { PCI_VENDOR_ID_RICOH, 0xe822, pci_func_0_dma_source },
> + { PCI_VENDOR_ID_RICOH, 0xe230, pci_func_0_dma_source },
> + { PCI_VENDOR_ID_RICOH, 0xe832, pci_func_0_dma_source },
> + { PCI_VENDOR_ID_RICOH, 0xe832, pci_func_0_dma_source },
> + { 0 }
> +};
> +
> +struct pci_dev *pci_dma_source(struct pci_dev *dev)
> +{
> + const struct pci_dev_dma_source *i;
> +
> + for (i = pci_dev_dma_source; i->dma_source; i++) {
> + if ((i->vendor == dev->vendor ||
> + i->vendor == (u16)PCI_ANY_ID) &&
> + (i->device == dev->device ||
> + i->device == (u16)PCI_ANY_ID))
> + return i->dma_source(dev);
> + }
> +
> + return dev;
> +}
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index d8c379d..5bc7502 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1486,9 +1486,14 @@ enum pci_fixup_pass {
>
> #ifdef CONFIG_PCI_QUIRKS
> void pci_fixup_device(enum pci_fixup_pass pass, struct pci_dev *dev);
> +struct pci_dev *pci_dma_source(struct pci_dev *dev);
> #else
> static inline void pci_fixup_device(enum pci_fixup_pass pass,
> struct pci_dev *dev) {}
> +static inline struct pci_dev *pci_dma_source(struct pci_dev *dev)
> +{
> + return dev;
> +}
> #endif
>
> void __iomem *pcim_iomap(struct pci_dev *pdev, int bar, unsigned long maxlen);
>
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