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[PATCH RFC 06/77] PCI/MSI: Factor out pci_get_msi_cap() interface

To: linux-kernel@vger.kernel.org
Subject: [PATCH RFC 06/77] PCI/MSI: Factor out pci_get_msi_cap() interface
From: Alexander Gordeev <agordeev@redhat.com>
Date: Wed, 2 Oct 2013 12:48:22 +0200
Cc: Alexander Gordeev <agordeev@redhat.com>, Bjorn Helgaas <bhelgaas@google.com>, Ralf Baechle <ralf@linux-mips.org>, Michael Ellerman <michael@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>, Dan Williams <dan.j.williams@intel.com>, Andy King <acking@vmware.com>, Jon Mason <jon.mason@intel.com>, Matt Porter <mporter@kernel.crashing.org>, linux-pci@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux390@de.ibm.com, linux-s390@vger.kernel.org, x86@kernel.org, linux-ide@vger.kernel.org, iss_storagedev@hp.com, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net, linux-driver@qlogic.com, Solarflare linux maintainers <linux-net-drivers@solarflare.com>, "VMware, Inc." <pv-drivers@vmware.com>, linux-scsi@vger.kernel.org
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This update is needed to facilitate a forthcoming re-design
MSI/MSI-X interrupts enabling pattern.

Device drivers will use this interface to obtain maximum number
of MSI interrupts the device supports and use that value in the
following call to pci_enable_msi_block() interface.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
---
 Documentation/PCI/MSI-HOWTO.txt |   15 +++++++++++++++
 drivers/pci/msi.c               |   33 +++++++++++++++++++++------------
 include/linux/pci.h             |    6 ++++++
 3 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index 35b2d64..1f37ce2 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -169,6 +169,21 @@ on any interrupt for which it previously called 
request_irq().
 Failure to do so results in a BUG_ON(), leaving the device with
 MSI enabled and thus leaking its vector.
 
+4.2.5 pci_get_msi_cap
+
+int pci_get_msi_cap(struct pci_dev *dev)
+
+This function could be used to retrieve the number of MSI vectors the
+device requested (via the Multiple Message Capable register). The MSI
+specification only allows the returned value to be a power of two,
+up to a maximum of 2^5 (32).
+
+If this function returns a negative number, it indicates the device is
+not capable of sending MSIs.
+
+If this function returns a positive number, it indicates the maximum
+number of MSI interrupt vectors that could be allocated.
+
 4.3 Using MSI-X
 
 The MSI-X capability is much more flexible than the MSI capability.
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 875c353..ca59bfc 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -812,6 +812,21 @@ static int pci_msi_check_device(struct pci_dev *dev, int 
nvec, int type)
        return 0;
 }
 
+int pci_get_msi_cap(struct pci_dev *dev)
+{
+       int ret;
+       u16 msgctl;
+
+       if (!dev->msi_cap)
+               return -EINVAL;
+
+       pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
+       ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+
+       return ret;
+}
+EXPORT_SYMBOL(pci_get_msi_cap);
+
 /**
  * pci_enable_msi_block - configure device's MSI capability structure
  * @dev: device to configure
@@ -828,13 +843,10 @@ static int pci_msi_check_device(struct pci_dev *dev, int 
nvec, int type)
 int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
 {
        int status, maxvec;
-       u16 msgctl;
 
-       if (!dev->msi_cap)
-               return -EINVAL;
-
-       pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
-       maxvec = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+       maxvec = pci_get_msi_cap(dev);
+       if (maxvec < 0)
+               return maxvec;
        if (nvec > maxvec)
                return maxvec;
 
@@ -859,13 +871,10 @@ EXPORT_SYMBOL(pci_enable_msi_block);
 int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec)
 {
        int ret, nvec;
-       u16 msgctl;
 
-       if (!dev->msi_cap)
-               return -EINVAL;
-
-       pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
-       ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+       ret = pci_get_msi_cap(dev);
+       if (ret < 0)
+               return ret;
 
        if (maxvec)
                *maxvec = ret;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index da172f9..2fa92ef 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1144,6 +1144,11 @@ struct msix_entry {
 
 
 #ifndef CONFIG_PCI_MSI
+static inline int pci_get_msi_cap(struct pci_dev *dev)
+{
+       return -1;
+}
+
 static inline int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
 {
        return -1;
@@ -1185,6 +1190,7 @@ static inline int pci_msi_enabled(void)
        return 0;
 }
 #else
+int pci_get_msi_cap(struct pci_dev *dev);
 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);
 void pci_msi_shutdown(struct pci_dev *dev);
-- 
1.7.7.6


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