linux-kernel - Re: [PATCH 1/5] pci: Add PCI DMA source ID quirk

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Message-ID: <4FC6204C.5000209@gmail.com>
Date:	Wed, 30 May 2012 21:27:40 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	benh@...nel.crashing.org, aik@...abs.ru,
	david@...son.dropbear.id.au, joerg.roedel@....com,
	dwmw2@...radead.org, konrad.wilk@...cle.com,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	ddutile@...hat.com
Subject: Re: [PATCH 1/5] pci: Add PCI DMA source ID quirk

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@...hat.com>
> ---
> 
>  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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