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

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Date:	Wed, 30 May 2012 12:05:24 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Jiang Liu <liuj97@...il.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

On Wed, 2012-05-30 at 21:27 +0800, Jiang Liu wrote:
> 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 for pointing this out Gerry.  I think I'll rename
pci_dma_source() to pci_get_dma_source() which will then increment the
reference of the device it returns, whether it's a quirk or the original
device.  The caller will then be responsible for doing a pci_dev_put().
Thanks,

Alex

> 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);
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 



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