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From: Alexander Gordeev <>
Cc: Ingo Molnar <>,
	Thomas Gleixner <>,
	Bjorn Helgaas <>,
	Suresh Siddha <>,
	Yinghai Lu <>, Jeff Garzik <>,
	Matthew Wilcox <>,,,
Subject: [PATCH v2 -tip 4/5] PCI, MSI: Enable multiple MSIs with pci_enable_msi_block_auto()
Date: Mon, 3 Sep 2012 11:19:40 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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 <>
 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
 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)
+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;
 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)
 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);

Alexander Gordeev

  parent reply	other threads:[~2012-09-03  9:19 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-03  9:16 [PATCH v2 -tip 0/5] x86, MSI, AHCI: Support multiple MSIs Alexander Gordeev
2012-09-03  9:17 ` [PATCH v2 -tip 1/5] x86, MSI: Support multiple MSIs in presense of IRQ remapping Alexander Gordeev
2012-09-03 18:53   ` Yinghai Lu
2012-09-04  9:32     ` Alexander Gordeev
2012-09-03  9:18 ` [PATCH v2 -tip 2/5] x86, MSI: Allocate as many multiple IRQs as requested Alexander Gordeev
2012-09-03  9:19 ` [PATCH v2 -tip 3/5] x86, MSI: Minor readability fixes Alexander Gordeev
2012-09-03  9:19 ` Alexander Gordeev [this message]
2012-09-07 20:53   ` [PATCH v2 -tip 4/5] PCI, MSI: Enable multiple MSIs with pci_enable_msi_block_auto() Bjorn Helgaas
2012-09-03  9:20 ` [PATCH v2 -tip 5/5] AHCI: Support multiple MSIs Alexander Gordeev
2012-09-27  4:59   ` Jeff Garzik
2012-09-26 12:38 ` [PATCH v2 -tip 0/5] x86, MSI, " Alexander Gordeev
2012-09-27  4:03   ` Ingo Molnar

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