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

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Date:	Wed, 30 May 2012 16:34:57 +0800
From:	Gavin Shan <shangw@...ux.vnet.ibm.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, alex.williamson@...hat.com
Subject: Re: [PATCH 1/5] pci: Add PCI DMA source ID quirk

Hi Alex,

>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));
>+}

I think we needn't retrieve the PCI device passed in again from the list
of PCI devices if its function number is zero.

	if (!PCI_FUNC(dev->devfn))
		return dev;

Thanks,
Gavin

>+
>+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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