pci: add pci_iomap_range

Virtio drivers should map the part of the BAR they need, not necessarily
all of it.

Cc: Bjorn Helgaas <[e-mail]>
Cc: [e-mail]
Acked-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

include/asm-generic/pci_iomap.h

···
 #ifdef CONFIG_PCI
 /* Create a virtual mapping cookie for a PCI BAR (memory or IO) */
 extern void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max);
+extern void __iomem *pci_iomap_range(struct pci_dev *dev, int bar,
+				     unsigned long offset,
+				     unsigned long maxlen);
 /* Create a virtual mapping cookie for a port on a given PCI device.
  * Do not call this directly, it exists to make it easier for architectures
  * to override */
···
 
 #elif defined(CONFIG_GENERIC_PCI_IOMAP)
 static inline void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max)
+{
+	return NULL;
+}
+
+static inline void __iomem *pci_iomap_range(struct pci_dev *dev, int bar,
+					    unsigned long offset,
+					    unsigned long maxlen)
 {
 	return NULL;
 }

lib/pci_iomap.c

···
 
 #ifdef CONFIG_PCI
 /**
+ * pci_iomap_range - create a virtual mapping cookie for a PCI BAR
+ * @dev: PCI device that owns the BAR
+ * @bar: BAR number
+ * @offset: map memory at the given offset in BAR
+ * @maxlen: max length of the memory to map
+ *
+ * Using this function you will get a __iomem address to your device BAR.
+ * You can access it using ioread*() and iowrite*(). These functions hide
+ * the details if this is a MMIO or PIO address space and will just do what
+ * you expect from them in the correct way.
+ *
+ * @maxlen specifies the maximum length to map. If you want to get access to
+ * the complete BAR from offset to the end, pass %0 here.
+ * */
+void __iomem *pci_iomap_range(struct pci_dev *dev,
+			      int bar,
+			      unsigned long offset,
+			      unsigned long maxlen)
+{
+	resource_size_t start = pci_resource_start(dev, bar);
+	resource_size_t len = pci_resource_len(dev, bar);
+	unsigned long flags = pci_resource_flags(dev, bar);
+
+	if (len <= offset || !start)
+		return NULL;
+	len -= offset;
+	start += offset;
+	if (maxlen && len > maxlen)
+		len = maxlen;
+	if (flags & IORESOURCE_IO)
+		return __pci_ioport_map(dev, start, len);
+	if (flags & IORESOURCE_MEM) {
+		if (flags & IORESOURCE_CACHEABLE)
+			return ioremap(start, len);
+		return ioremap_nocache(start, len);
+	}
+	/* What? */
+	return NULL;
+}
+EXPORT_SYMBOL(pci_iomap_range);
+
+/**
  * pci_iomap - create a virtual mapping cookie for a PCI BAR
  * @dev: PCI device that owns the BAR
  * @bar: BAR number
···
  * */
 void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
 {
-	resource_size_t start = pci_resource_start(dev, bar);
-	resource_size_t len = pci_resource_len(dev, bar);
-	unsigned long flags = pci_resource_flags(dev, bar);
-
-	if (!len || !start)
-		return NULL;
-	if (maxlen && len > maxlen)
-		len = maxlen;
-	if (flags & IORESOURCE_IO)
-		return __pci_ioport_map(dev, start, len);
-	if (flags & IORESOURCE_MEM) {
-		if (flags & IORESOURCE_CACHEABLE)
-			return ioremap(start, len);
-		return ioremap_nocache(start, len);
-	}
-	/* What? */
-	return NULL;
+	return pci_iomap_range(dev, bar, 0, maxlen);
 }
-
 EXPORT_SYMBOL(pci_iomap);
 #endif /* CONFIG_PCI */