PCI: Add helper function msi_desc_to_pci_sysdata()

Add helper function msi_desc_to_pci_sysdata() to retrieve sysdata from
an MSI descriptor. To avoid pulling include/linux/pci.h into
include/linux/msi.h, msi_desc_to_pci_sysdata() is implemented as a normal
function instead of an inline function.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Reviewed-by: Yijing Wang <wangyijing@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Stuart Yoder <stuart.yoder@freescale.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Alexander Gordeev <agordeev@redhat.com>
Link: http://lkml.kernel.org/r/1436428847-8886-2-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/pci/msi.c

@@ -1137,6 +1137,14 @@ int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
 }
 EXPORT_SYMBOL(pci_enable_msix_range);
 
+void *msi_desc_to_pci_sysdata(struct msi_desc *desc)
+{
+	struct pci_dev *dev = msi_desc_to_pci_dev(desc);
+
+	return dev->bus->sysdata;
+}
+EXPORT_SYMBOL_GPL(msi_desc_to_pci_sysdata);
+
 #ifdef CONFIG_PCI_MSI_IRQ_DOMAIN
 /**
  * pci_msi_domain_write_msg - Helper to write MSI message to PCI config space

include/linux/msi.h

@@ -60,6 +60,13 @@ static inline struct pci_dev *msi_desc_to_pci_dev(struct msi_desc *desc)
 {
 	return desc->dev;
 }
+
+void *msi_desc_to_pci_sysdata(struct msi_desc *desc);
+#else /* CONFIG_PCI_MSI */
+static inline void *msi_desc_to_pci_sysdata(struct msi_desc *desc)
+{
+	return NULL;
+}
 #endif /* CONFIG_PCI_MSI */
 
 void __pci_read_msi_msg(struct msi_desc *entry, struct msi_msg *msg);