PCI/MSI: Move pci_disable_msi() to api.c

msi.c is a maze of randomly sorted functions which makes the code
unreadable. As a first step split the driver visible API and the internal
implementation which also allows proper API documentation via one file.

Create drivers/pci/msi/api.c to group all exported device-driver PCI/MSI
APIs in one C file.

Begin by moving pci_disable_msi() there and add kernel-doc for the function
as appropriate.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20221111122014.696798036@linutronix.de

drivers/pci/msi/Makefile

@@ -2,6 +2,5 @@
 #
 # Makefile for the PCI/MSI
 obj-$(CONFIG_PCI)			+= pcidev_msi.o
-obj-$(CONFIG_PCI_MSI)			+= msi.o
-obj-$(CONFIG_PCI_MSI)			+= irqdomain.o
+obj-$(CONFIG_PCI_MSI)			+= api.o msi.o irqdomain.o
 obj-$(CONFIG_PCI_MSI_ARCH_FALLBACKS)	+= legacy.o

drivers/pci/msi/api.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI MSI/MSI-X — Exported APIs for device drivers
+ *
+ * Copyright (C) 2003-2004 Intel
+ * Copyright (C) Tom Long Nguyen (tom.l.nguyen@intel.com)
+ * Copyright (C) 2016 Christoph Hellwig.
+ * Copyright (C) 2022 Linutronix GmbH
+ */
+
+#include <linux/export.h>
+
+#include "msi.h"
+
+/**
+ * pci_disable_msi() - Disable MSI interrupt mode on device
+ * @dev: the PCI device to operate on
+ *
+ * Legacy device driver API to disable MSI interrupt mode on device,
+ * free earlier allocated interrupt vectors, and restore INTx emulation.
+ * The PCI device Linux IRQ (@dev->irq) is restored to its default
+ * pin-assertion IRQ. This is the cleanup pair of pci_enable_msi().
+ *
+ * NOTE: The newer pci_alloc_irq_vectors() / pci_free_irq_vectors() API
+ * pair should, in general, be used instead.
+ */
+void pci_disable_msi(struct pci_dev *dev)
+{
+	if (!pci_msi_enabled() || !dev || !dev->msi_enabled)
+		return;
+
+	msi_lock_descs(&dev->dev);
+	pci_msi_shutdown(dev);
+	pci_free_msi_irqs(dev);
+	msi_unlock_descs(&dev->dev);
+}
+EXPORT_SYMBOL(pci_disable_msi);

drivers/pci/msi/msi.c

@@ -163,7 +163,7 @@ void pci_write_msi_msg(unsigned int irq, struct msi_msg *msg)
 }
 EXPORT_SYMBOL_GPL(pci_write_msi_msg);
 
-static void free_msi_irqs(struct pci_dev *dev)
+void pci_free_msi_irqs(struct pci_dev *dev)
 {
 	pci_msi_teardown_msi_irqs(dev);
 
@@ -413,7 +413,7 @@ static int msi_capability_init(struct pci_dev *dev, int nvec,
 
 err:
 	pci_msi_unmask(entry, msi_multi_mask(entry));
-	free_msi_irqs(dev);
+	pci_free_msi_irqs(dev);
 fail:
 	dev->msi_enabled = 0;
 unlock:
@@ -531,7 +531,7 @@ static int msix_setup_interrupts(struct pci_dev *dev, void __iomem *base,
 	goto out_unlock;
 
 out_free:
-	free_msi_irqs(dev);
+	pci_free_msi_irqs(dev);
 out_unlock:
 	msi_unlock_descs(&dev->dev);
 	kfree(masks);
@@ -680,7 +680,7 @@ int pci_msi_vec_count(struct pci_dev *dev)
 }
 EXPORT_SYMBOL(pci_msi_vec_count);
 
-static void pci_msi_shutdown(struct pci_dev *dev)
+void pci_msi_shutdown(struct pci_dev *dev)
 {
 	struct msi_desc *desc;
 
@@ -701,18 +701,6 @@ static void pci_msi_shutdown(struct pci_dev *dev)
 	pcibios_alloc_irq(dev);
 }
 
-void pci_disable_msi(struct pci_dev *dev)
-{
-	if (!pci_msi_enable || !dev || !dev->msi_enabled)
-		return;
-
-	msi_lock_descs(&dev->dev);
-	pci_msi_shutdown(dev);
-	free_msi_irqs(dev);
-	msi_unlock_descs(&dev->dev);
-}
-EXPORT_SYMBOL(pci_disable_msi);
-
 /**
  * pci_msix_vec_count - return the number of device's MSI-X table entries
  * @dev: pointer to the pci_dev data structure of MSI-X device function
@@ -797,7 +785,7 @@ void pci_disable_msix(struct pci_dev *dev)
 
 	msi_lock_descs(&dev->dev);
 	pci_msix_shutdown(dev);
-	free_msi_irqs(dev);
+	pci_free_msi_irqs(dev);
 	msi_unlock_descs(&dev->dev);
 }
 EXPORT_SYMBOL(pci_disable_msix);

drivers/pci/msi/msi.h

@@ -84,6 +84,10 @@ static inline __attribute_const__ u32 msi_multi_mask(struct msi_desc *desc)
 	return (1 << (1 << desc->pci.msi_attrib.multi_cap)) - 1;
 }
 
+/* MSI internal functions invoked from the public APIs */
+void pci_msi_shutdown(struct pci_dev *dev);
+void pci_free_msi_irqs(struct pci_dev *dev);
+
 /* Legacy (!IRQDOMAIN) fallbacks */
 #ifdef CONFIG_PCI_MSI_ARCH_FALLBACKS
 int pci_msi_legacy_setup_msi_irqs(struct pci_dev *dev, int nvec, int type);