src/devices/pci_device.c

/*
 *      PCI Bus Services, see include/linux/pci.h for further explanation.
 *
 *      Copyright 1993 -- 1997 Drew Eckhardt, Frederic Potter,
 *      David Mosberger-Tang
 *
 *      Copyright 1997 -- 1999 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 *	
 *	Copyright 2003 -- Eric Biederman <ebiederman@lnxi.com>
 */

#include <console/console.h>
#include <stdlib.h>
#include <stdint.h>
#include <bitops.h>
#include <string.h>
#include <arch/io.h>
#include <device/device.h>
#include <device/pci.h>
#include <device/pci_ids.h>
#include <device/chip.h>
#include <part/hard_reset.h>
#include <part/fallback_boot.h>

/** Given a device and register, read the size of the BAR for that register. 
 * @param dev       Pointer to the device structure
 * @param resource  Pointer to the resource structure
 * @param index     Address of the pci configuration register
 */
static struct resource *pci_get_resource(struct device *dev, unsigned long index)
{
	struct resource *resource;
	uint32_t addr, size, base;
	unsigned long type;

	/* Initialize the resources to nothing */
	resource = get_resource(dev, index);

	addr = pci_read_config32(dev, index);

	/* FIXME: more consideration for 64-bit PCI devices,
	 * we currently detect their size but otherwise
	 * treat them as 32-bit resources
	 */
	/* get the size */
	pci_write_config32(dev, index, ~0);
	size = pci_read_config32(dev,  index);

	/* get the minimum value the bar can be set to */
	pci_write_config32(dev, index, 0);
	base = pci_read_config32(dev, index);

	/* restore addr */
	pci_write_config32(dev, index, addr);

	/*
	 * some broken hardware has read-only registers that do not 
	 * really size correctly. You can tell this if addr == size
	 * Example: the acer m7229 has BARs 1-4 normally read-only. 
	 * so BAR1 at offset 0x10 reads 0x1f1. If you size that register
	 * by writing 0xffffffff to it, it will read back as 0x1f1 -- a 
	 * violation of the spec. 
	 * We catch this case and ignore it by settting size and type to 0.
	 * This incidentally catches the common case where registers 
	 * read back as 0 for both address and size. 
	 */
	if ((addr == size) && (addr == base)) {
		if (size != 0) {
			printk_debug(
				"%s register %02x(%08x), read-only ignoring it\n",
				dev_path(dev),
				index, addr);
		}
		resource->flags = 0;
	}
	/* Now compute the actual size, See PCI Spec 6.2.5.1 ...  */
	else if (size & PCI_BASE_ADDRESS_SPACE_IO) {
		type = size & (~PCI_BASE_ADDRESS_IO_MASK);
		/* BUG! Top 16 bits can be zero (or not) 
		 * So set them to 0xffff so they go away ...
		 */
		resource->size = (~((size | 0xffff0000) & PCI_BASE_ADDRESS_IO_MASK)) +1;
		resource->align = log2(resource->size);
		resource->gran = resource->align;
		resource->flags |= IORESOURCE_IO;
		resource->limit = 0xffff;
	} 
	else {
		/* A Memory mapped base address */
		type = size & (~PCI_BASE_ADDRESS_MEM_MASK);
		resource->size = (~(size &PCI_BASE_ADDRESS_MEM_MASK)) +1;
		resource->align = log2(resource->size);
		resource->gran = resource->align;
		resource->flags |= IORESOURCE_MEM;
		if (type & PCI_BASE_ADDRESS_MEM_PREFETCH) {
			resource->flags |= IORESOURCE_PREFETCH;
		}
		type &= PCI_BASE_ADDRESS_MEM_TYPE_MASK;
		if (type == PCI_BASE_ADDRESS_MEM_TYPE_32) {
			/* 32bit limit */
			resource->limit = 0xffffffffUL;
		}
		else if (type == PCI_BASE_ADDRESS_MEM_TYPE_1M) {
			/* 1MB limit */
			resource->limit = 0x000fffffUL;
		}
		else if (type == PCI_BASE_ADDRESS_MEM_TYPE_64) {
			unsigned long index_hi;
			/* 64bit limit 
			 * For now just treat this as a 32bit limit
			 */
			index_hi = index + 4;
			resource->limit = 0xffffffffUL;
			resource->flags |= IORESOURCE_PCI64;
			addr = pci_read_config32( dev, index_hi);
			/* get the extended size */
			pci_write_config32(dev, index_hi, 0xffffffffUL);
			size = pci_read_config32( dev, index_hi);

			/* get the minimum value the bar can be set to */
			pci_write_config32(dev, index_hi, 0);
			base = pci_read_config32(dev,  index_hi);

			/* restore addr */
			pci_write_config32(dev, index_hi, addr);
			
			if ((size == 0xffffffff) && (base == 0)) {
				/* Clear the top half of the bar */
				pci_write_config32(dev, index_hi, 0);
			}
			else {
				printk_err("%s Unable to handle 64-bit address\n",
					dev_path(dev));
				resource->flags = IORESOURCE_PCI64;
			}
		} 
		else {
			/* Invalid value */
			resource->flags = 0;
		}
	}
	/* dev->size holds the flags... */
	return resource;
}

/** Read the base address registers for a given device. 
 * @param dev Pointer to the dev structure
 * @param howmany How many registers to read (6 for device, 2 for bridge)
 */
static void pci_read_bases(struct device *dev, unsigned int howmany)
{
	unsigned long index;

	for (index = PCI_BASE_ADDRESS_0; (index < PCI_BASE_ADDRESS_0 + (howmany << 2)); ) {
		struct resource *resource;
		resource = pci_get_resource(dev, index);
		index += (resource->flags & IORESOURCE_PCI64)?8:4;
	}
	compact_resources(dev);
}

static void pci_bridge_read_bases(struct device *dev)
{
	struct resource *resource;

	/* FIXME handle bridges without some of the optional resources */

	/* Initialize the io space constraints on the current bus */
	resource = get_resource(dev, PCI_IO_BASE);
	resource->size  = 0;
	resource->align = log2(PCI_IO_BRIDGE_ALIGN);
	resource->gran  = log2(PCI_IO_BRIDGE_ALIGN);
	resource->limit = 0xffffUL;
	resource->flags |= IORESOURCE_IO | IORESOURCE_PCI_BRIDGE;
	compute_allocate_resource(&dev->link[0], resource,
				  IORESOURCE_IO, IORESOURCE_IO);

	/* Initiliaze the prefetchable memory constraints on the current bus */
	resource = get_resource(dev, PCI_PREF_MEMORY_BASE);
	resource->size = 0;
	resource->align = log2(PCI_MEM_BRIDGE_ALIGN);
	resource->gran  = log2(PCI_MEM_BRIDGE_ALIGN);
	resource->limit = 0xffffffffUL;
	resource->flags = IORESOURCE_MEM | IORESOURCE_PREFETCH | IORESOURCE_PCI_BRIDGE;
	resource->index = PCI_PREF_MEMORY_BASE;
	compute_allocate_resource(&dev->link[0], resource,
				  IORESOURCE_MEM | IORESOURCE_PREFETCH, 
				  IORESOURCE_MEM | IORESOURCE_PREFETCH);

	/* Initialize the memory resources on the current bus */
	resource = get_resource(dev, PCI_MEMORY_BASE);
	resource->size = 0;
	resource->align = log2(PCI_MEM_BRIDGE_ALIGN);
	resource->gran  = log2(PCI_MEM_BRIDGE_ALIGN);
	resource->limit = 0xffffffffUL;
	resource->flags = IORESOURCE_MEM | IORESOURCE_PCI_BRIDGE;
	compute_allocate_resource(&dev->link[0], resource,
				  IORESOURCE_MEM | IORESOURCE_PREFETCH,
				  IORESOURCE_MEM);

	compact_resources(dev);
}

void pci_dev_read_resources(struct device *dev)
{
	uint32_t addr;

	pci_read_bases(dev, 6);

	addr = pci_read_config32(dev, PCI_ROM_ADDRESS);
	dev->rom_address = (addr == 0xffffffff)? 0 : addr;
}

void pci_bus_read_resources(struct device *dev)
{
	uint32_t addr;

	pci_bridge_read_bases(dev);
	pci_read_bases(dev, 2);
	
	addr = pci_read_config32(dev, PCI_ROM_ADDRESS1);
	dev->rom_address = (addr == 0xffffffff)? 0 : addr;
}

/**
 * @brief round a number up to an alignment. 
 * @param val the starting value
 * @param roundup Alignment as a power of two
 * @returns rounded up number
 */
static unsigned long round(unsigned long val, unsigned long roundup)
{
	/* ROUNDUP MUST BE A POWER OF TWO. */
	unsigned long inverse;
	inverse = ~(roundup - 1);
	val += (roundup - 1);
	val &= inverse;
	return val;
}

static void pci_set_resource(struct device *dev, struct resource *resource)
{
	unsigned long base, limit;
	unsigned char buf[10];
	unsigned long gran;

	/* Make certain the resource has actually been set */

	if (!(resource->flags & IORESOURCE_ASSIGNED)) {
		printk_err("ERROR: %s %02x not allocated\n",
			   dev_path(dev), resource->index);
		return;
	}

	/* If I have already stored this resource don't worry about it */
	if (resource->flags & IORESOURCE_STORED) {
		return;
	}

	/* Only handle PCI memory and IO resources for now */
	if (!(resource->flags & (IORESOURCE_MEM |IORESOURCE_IO)))
		return;

	if (resource->flags & IORESOURCE_MEM) {
		dev->command |= PCI_COMMAND_MEMORY;
	}
	if (resource->flags & IORESOURCE_IO) {
		dev->command |= PCI_COMMAND_IO;
	}
	if (resource->flags & IORESOURCE_PCI_BRIDGE) {
		dev->command |= PCI_COMMAND_MASTER;
	}

	/* Get the base address */
	base = resource->base;

	/* Get the resource granularity */
	gran = 1UL << resource->gran;

	/* For a non bridge resource granularity and alignment are the same.
	 * For a bridge resource align is the largest needed alignment below
	 * the bridge.  While the granularity is simply how many low bits of the
	 * address cannot be set.
	 */
	
	/* Get the limit (rounded up) */
	limit = base + round(resource->size, gran) - 1UL;
	
	/* Now store the resource */
	resource->flags |= IORESOURCE_STORED;
	if (!(resource->flags & IORESOURCE_PCI_BRIDGE)) {
		/* some chipsets allow us to set/clear the IO bit. 
		 * (e.g. VIA 82c686a.) So set it to be safe) */
		limit = base + resource->size -1;
		if (resource->flags & IORESOURCE_IO) {
			base |= PCI_BASE_ADDRESS_SPACE_IO;
		}
		pci_write_config32(dev, resource->index, base & 0xffffffff);
		if (resource->flags & IORESOURCE_PCI64) {
			/* FIXME handle real 64bit base addresses */
			pci_write_config32(dev, resource->index + 4, 0);
		}
	} else if (resource->index == PCI_IO_BASE) {
		/* set the IO ranges
		 * WARNING: we don't really do 32-bit addressing for IO yet! 
		 */
		compute_allocate_resource(&dev->link[0], resource, 
					  IORESOURCE_IO, IORESOURCE_IO);
		pci_write_config8(dev, PCI_IO_BASE,  base >> 8);
		pci_write_config8(dev, PCI_IO_LIMIT, limit >> 8);
		pci_write_config16(dev, PCI_IO_BASE_UPPER16, 0);
		pci_write_config16(dev, PCI_IO_LIMIT_UPPER16, 0);
	} else if (resource->index == PCI_MEMORY_BASE) {
		/* set the memory range */
		compute_allocate_resource(&dev->link[0], resource,
					  IORESOURCE_MEM | IORESOURCE_PREFETCH, 
					  IORESOURCE_MEM);
		pci_write_config16(dev, PCI_MEMORY_BASE, base >> 16);
		pci_write_config16(dev, PCI_MEMORY_LIMIT, limit >> 16);
	} else if (resource->index == PCI_PREF_MEMORY_BASE) {
		/* set the prefetchable memory range
		 * WARNING: we don't really do 64-bit addressing for
		 * prefetchable memory yet! */
		compute_allocate_resource(&dev->link[0], resource,
					  IORESOURCE_MEM | IORESOURCE_PREFETCH, 
					  IORESOURCE_MEM | IORESOURCE_PREFETCH);
		pci_write_config16(dev, PCI_PREF_MEMORY_BASE,  base >> 16);
		pci_write_config16(dev, PCI_PREF_MEMORY_LIMIT, limit >> 16);
		pci_write_config32(dev, PCI_PREF_BASE_UPPER32, 0);
		pci_write_config32(dev, PCI_PREF_LIMIT_UPPER32, 0);
	} else {
		/* Don't let me think I stored the resource */
		resource->flags &= ~IORESOURCE_STORED;
		printk_err("ERROR: invalid resource->index %x\n",
			   resource->index);
	}

	buf[0] = '\0';
	if (resource->flags & IORESOURCE_PCI_BRIDGE) {
		sprintf(buf, "bus %d ", dev->link[0].secondary);
	}
	printk_debug("%s %02x <- [0x%08lx - 0x%08lx] %s%s\n",
		     dev_path(dev), resource->index, resource->base,
		     limit, buf,
		     (resource->flags & IORESOURCE_IO)? "io":
		     (resource->flags & IORESOURCE_PREFETCH)? "prefmem": "mem");
	return;
}

void pci_dev_set_resources(struct device *dev)
{
	struct resource *resource, *last;
	unsigned link;
	uint8_t line;

	last = &dev->resource[dev->resources];
	for (resource = &dev->resource[0]; resource < last; resource++) {
		pci_set_resource(dev, resource);
	}

	for (link = 0; link < dev->links; link++) {
		struct bus *bus;
		bus = &dev->link[link];
		if (bus->children) {
			assign_resources(bus);
		}
	}

	/* set a default latency timer */
	pci_write_config8(dev, PCI_LATENCY_TIMER, 0x40);

	/* set a default secondary latency timer */
	if ((dev->hdr_type & 0x7f) == PCI_HEADER_TYPE_BRIDGE) {
		pci_write_config8(dev, PCI_SEC_LATENCY_TIMER, 0x40);
	}

	/* zero the irq settings */
	line = pci_read_config8(dev, PCI_INTERRUPT_PIN);
	if (line) {
		pci_write_config8(dev, PCI_INTERRUPT_LINE, 0);
	}
	/* set the cache line size, so far 64 bytes is good for everyone */
	pci_write_config8(dev, PCI_CACHE_LINE_SIZE, 64 >> 2);
}

void pci_dev_enable_resources(struct device *dev)
{
	uint16_t command;
	command = pci_read_config16(dev, PCI_COMMAND);
	command |= dev->command;
	command |= (PCI_COMMAND_PARITY + PCI_COMMAND_SERR); /* error check */
	printk_debug("%s cmd <- %02x\n", dev_path(dev), command);
	pci_write_config16(dev, PCI_COMMAND, command);

	enable_childrens_resources(dev);
}

void pci_bus_enable_resources(struct device *dev)
{
	uint16_t ctrl;
	ctrl = pci_read_config16(dev, PCI_BRIDGE_CONTROL);
	ctrl |= dev->link[0].bridge_ctrl;
	ctrl |= (PCI_BRIDGE_CTL_PARITY + PCI_BRIDGE_CTL_SERR); /* error check */
	printk_debug("%s bridge ctrl <- %04x\n", dev_path(dev), ctrl);
	pci_write_config16(dev, PCI_BRIDGE_CONTROL, ctrl);

	pci_dev_enable_resources(dev);
}

/** Default device operation for PCI devices */
struct device_operations default_pci_ops_dev = {
	.read_resources   = pci_dev_read_resources,
	.set_resources    = pci_dev_set_resources,
	.enable_resources = pci_dev_enable_resources,
	.init		  = 0,
	.scan_bus	  = 0,
};

/** Default device operations for PCI bridges */
struct device_operations default_pci_ops_bus = {
	.read_resources   = pci_bus_read_resources,
	.set_resources    = pci_dev_set_resources,
	.enable_resources = pci_bus_enable_resources,
	.init		  = 0,
	.scan_bus	  = pci_scan_bridge,
};

/**
 * @brief Set up PCI device operation
 *
 *
 * @param dev 
 *
 * @see pci_drivers
 */
static void set_pci_ops(struct device *dev)
{
	struct pci_driver *driver;

	if (dev->ops) {
		return;
	}

	/* Look through the list of setup drivers and find one for
	 * this pci device */
	for (driver = &pci_drivers[0]; driver != &epci_drivers[0]; driver++) {
		if ((driver->vendor == dev->vendor) &&
		    (driver->device == dev->device)) {
			dev->ops = driver->ops;

			printk_debug("%s [%04x/%04x] %sops\n", dev_path(dev),
				     driver->vendor, driver->device,
				     (driver->ops->scan_bus?"bus ":""));

			return;
		}
	}

#if 0
	extern struct pci_driver generic_vga_driver;
	/* TODO: Install generic VGA driver for VGA devices, base on the
	 * class ID */
	if ((dev->class >> 8)  == PCI_CLASS_DISPLAY_VGA) {
		printk_debug("setting up generic VGA driver\n");
		dev->ops = generic_vga_driver.ops;
		return;
	}
#endif

	/* If I don't have a specific driver use the default operations */
	switch(dev->hdr_type & 0x7f) {	/* header type */
	case PCI_HEADER_TYPE_NORMAL:	/* standard header */
		if ((dev->class >> 8) == PCI_CLASS_BRIDGE_PCI)
			goto bad;
		dev->ops = &default_pci_ops_dev;
		break;
	case PCI_HEADER_TYPE_BRIDGE:
		if ((dev->class >> 8) != PCI_CLASS_BRIDGE_PCI)
			goto bad;
		dev->ops = &default_pci_ops_bus;
		break;
	default:
	bad:
		if (dev->enabled) {
			printk_err("%s [%04x/%04x/%06x] has unknown header "
				   "type %02x, ignoring.\n",
				   dev_path(dev),
				   dev->vendor, dev->device, 
				   dev->class >> 8, dev->hdr_type);
		}
	}
	return;
}

/**
 * @brief Find a specific device structure on a list of device structures
 *
 * Given a linked list of PCI device structures and a devfn number, find the
 * device structure correspond to the devfn.
 *
 * @param list the device structure list
 * @param devfn a device/function number
 *
 * @return pointer to the device structure found
 */
static struct device *pci_scan_get_dev(struct device **list,
				       unsigned int devfn)
{
	struct device *dev = 0;

	printk_debug("%s, looking for devfn: %02x.%01x\n", __FUNCTION__,
		     devfn >> 3, devfn & 7);
	for (; *list; list = &(*list)->sibling) {
		if ((*list)->path.type != DEVICE_PATH_PCI) {
			printk_err("child %s not a pci device\n",
				   dev_path(*list));
			continue;
		}
		if ((*list)->path.u.pci.devfn == devfn) {
			/* Unlink from the list */
			dev = *list;
			*list = (*list)->sibling;
			dev->sibling = 0;
			break;
		}
	}

	printk_debug("%s, found dev %08x\n", __FUNCTION__, dev);

	/* FIXME: why are we doing this ? Isn't there some order between the
	 * structures before ? */
	if (dev) {
		device_t child;
		/* Find the last child of our parent */
		for (child = dev->bus->children; child && child->sibling; ) {
			child = child->sibling;
		}
		/* Place the device on the list of children of it's parent. */
		if (child) {
			child->sibling = dev;
		} else {
			dev->bus->children = dev;
		}
	}

	return dev;
}

/**
 * @brief Scan a PCI bus
 *
 * Determine the existence of devices and bridges on a PCI bus. If there are
 * bridges on the bus, recursively scan the buses behind the bridges.
 *
 * This function is the default scan_bus() method for the root device
 * 'dev_root'.
 *
 * @param bus pointer to the bus structure
 * @param min_devfn minimum devfn to look at in the scan usually 0x00
 * @param max_devfn maximum devfn to look at in the scan usually 0xff
 * @param max current bus number
 *
 * @return The maximum bus number found, after scanning all subordinate busses
 */
unsigned int pci_scan_bus(struct bus *bus, unsigned min_devfn,
			  unsigned max_devfn, unsigned int max)
{
	unsigned int devfn;
	device_t dev;
	device_t old_devices;
	device_t child;

	printk_debug("PCI: pci_scan_bus for bus %d\n", bus->secondary);

	old_devices = bus->children;
	bus->children = 0;

	post_code(0x24);

	/* probe all devices/functions on this bus with some optimization for
	 * non-existence and single funcion devices */
	for (devfn = min_devfn; devfn <= max_devfn; devfn++) {
		uint32_t id, class;
		uint8_t hdr_type;

		/* device structures for PCI devices associated with static
		 * devices are already created during the static device
		 * enumeration, find out if it is the case for this devfn */
		dev = pci_scan_get_dev(&old_devices, devfn);

		if (!dev) {
			/* it's not associated with a static device, detect if
			 * this device is present */
			struct device dummy;
			dummy.bus              = bus;
			dummy.path.type        = DEVICE_PATH_PCI;
			dummy.path.u.pci.devfn = devfn;
			id = pci_read_config32(&dummy, PCI_VENDOR_ID);
			/* some broken boards return 0 if a slot is empty: */
			if ((id == 0xffffffff) || (id == 0x00000000) || 
			    (id == 0x0000ffff) || (id == 0xffff0000)) {
				printk_spew("PCI: devfn 0x%x, bad id 0x%x\n",
					    devfn, id);
				if (PCI_FUNC(devfn) == 0x00) {
					/* if this is a function 0 device and
					 * it is not present, skip to next
					 * device */
					devfn += 0x07;
				}
				/* this function in a multi function device is
				 * not present, skip to next function */
				continue;
			}
			dev = alloc_dev(bus, &dummy.path);
		} else {
			/* Run the magic enable/disable sequence for the
			 * device */
			/* FIXME: What happen if this PCI device listed as
			 * static device but does not exist ? This calls
			 * some arbitray code without any justification
			 * Also, it calls the enable function regardlessly
			 * the value of dev->enabled  */
			if (dev->chip && dev->chip->control &&
			    dev->chip->control->enable_dev) {
				int enabled  = dev->enabled;
				dev->enabled = 1;
				dev->chip->control->enable_dev(dev);
				dev->enabled = enabled;
			}
			/* Now read the vendor and device id */
			id = pci_read_config32(dev, PCI_VENDOR_ID);
		}
		/* Read the rest of the pci configuration information */
		hdr_type = pci_read_config8(dev, PCI_HEADER_TYPE);
		class = pci_read_config32(dev, PCI_CLASS_REVISION);

		/* Store the interesting information in the device structure */
		dev->vendor = id & 0xffff;
		dev->device = (id >> 16) & 0xffff;
		dev->hdr_type = hdr_type;
		/* class code, the upper 3 bytes of PCI_CLASS_REVISION */
		dev->class = class >> 8;

		/* Look at the vendor and device id, or at least the 
		 * header type and class and figure out which set of
		 * configuration methods to use.  Unless we already
		 * have some pci ops.
		 */
		set_pci_ops(dev);
		/* Error if we don't have some pci operations for it */
		if (!dev->ops) {
			printk_err("%s No device operations\n",
				   dev_path(dev));
			continue;
		}

		/* Now run the magic enable/disable sequence for the device */
		if (dev->ops && dev->ops->enable) {
			dev->ops->enable(dev);
		} else if (dev->chip && dev->chip->control &&
			   dev->chip->control->enable_dev) {
			dev->chip->control->enable_dev(dev);
		}

		printk_debug("%s [%04x/%04x] %s\n", 
			     dev_path(dev),
			     dev->vendor, dev->device, 
			     dev->enabled?"enabled": "disabled");

		if (PCI_FUNC(devfn) == 0x00 && (hdr_type & 0x80) != 0x80) {
			/* if this is not a multi function device, don't
			 * waste time probe another function.
			 * Skip to next device. */
			devfn += 0x07;
		}
	}
	post_code(0x25);

	/* if a child provides scan_bus(), for example a bridge, scan
	 * buses behind that child */
	for (child = bus->children; child; child = child->sibling) {
		// make sure that we have an ops structure
		if (!child->ops) {
			continue;
		}
		if (!child->ops->scan_bus) {
			continue;
		}
		max = child->ops->scan_bus(child, max);
	}

	/*
	 * We've scanned the bus and so we know all about what's on
	 * the other side of any bridges that may be on this bus plus
	 * any devices.
	 *
	 * Return how far we've got finding sub-buses.
	 */
	printk_debug("PCI: pci_scan_bus returning with max=%02x\n", max);
	post_code(0x55);
	return max;
}

/**
 * @brief Scan a PCI bridge and the buses behind the bridge.
 *
 * Determine the existence of buses behind the bridge. Set up the bridge
 * according to the result of the scan.
 *
 * This function is the default scan_bus() method for PCI bridge devices.
 *
 * @param dev pointer to the bridge device
 * @param max the highest bus number assgined up to now
 *
 * @return The maximum bus number found, after scanning all subordinate busses
 */
unsigned int pci_scan_bridge(struct device *dev, unsigned int max)
{
	struct bus *bus;
	uint32_t buses;
	uint16_t cr;

	bus = &dev->link[0];
	dev->links = 1;

	/* Set up the primary, secondary and subordinate bus numbers. We have
	 * no idea how many buses are behind this bridge yet, so we set the
	 * subordinate bus number to 0xff for the moment. */
	bus->secondary = ++max;
	bus->subordinate = 0xff;

	/* Clear all status bits and turn off memory, I/O and master enables. */
	cr = pci_read_config16(dev, PCI_COMMAND);
	pci_write_config16(dev, PCI_COMMAND, 0x0000);
	pci_write_config16(dev, PCI_STATUS, 0xffff);

	/* Read the existing primary/secondary/subordinate bus
	 * number configuration. */
	buses = pci_read_config32(dev, PCI_PRIMARY_BUS);

	/* Configure the bus numbers for this bridge: the configuration
	 * transactions will not be propagated by the bridge if it is not
	 * correctly configured */
	buses &= 0xff000000;
	buses |= (((unsigned int) (dev->bus->secondary) << 0) |
		  ((unsigned int) (bus->secondary) << 8) |
		  ((unsigned int) (bus->subordinate) << 16));
	pci_write_config32(dev, PCI_PRIMARY_BUS, buses);

	/* Now we can scan all subordinate buses i.e. the buses behind the
	 * bridge */
	max = pci_scan_bus(bus, 0x00, 0xff, max);

	/* We know the number of buses behind this bridge. Set the subordinate
	 * bus number to its real value */
	bus->subordinate = max;
	buses = (buses & 0xff00ffff) |
		((unsigned int) (bus->subordinate) << 16);
	pci_write_config32(dev, PCI_PRIMARY_BUS, buses);
	pci_write_config16(dev, PCI_COMMAND, cr);

	printk_spew("%s returns max %d\n", __FUNCTION__, max);
	return max;
}

/*
    Tell the EISA int controller this int must be level triggered
    THIS IS A KLUDGE -- sorry, this needs to get cleaned up.
*/
static void pci_level_irq(unsigned char intNum)
{
	unsigned short intBits = inb(0x4d0) | (((unsigned) inb(0x4d1)) << 8);

	printk_debug("%s: current ints are 0x%x\n", __FUNCTION__, intBits);
	intBits |= (1 << intNum);

	printk_debug("%s: try to set ints 0x%x\n", __FUNCTION__, intBits);

	// Write new values
	outb((unsigned char) intBits, 0x4d0);
	outb((unsigned char) (intBits >> 8), 0x4d1);

	/* this seems like an error but is not ... */
#if 1
	if (inb(0x4d0) != (intBits & 0xf)) {
	  printk_err("%s: lower order bits are wrong: want 0x%x, got 0x%x\n",
		     __FUNCTION__, intBits &0xf, inb(0x4d0));
	}
	if (inb(0x4d1) != ((intBits >> 8) & 0xf)) {
	  printk_err("%s: lower order bits are wrong: want 0x%x, got 0x%x\n",
		     __FUNCTION__, (intBits>>8) &0xf, inb(0x4d1));
	}
#endif
}

/*
    This function assigns IRQs for all functions contained within
    the indicated device address.  If the device does not exist or does
    not require interrupts then this function has no effect.

    This function should be called for each PCI slot in your system.  

    pIntAtoD is an array of IRQ #s that are assigned to PINTA through PINTD of
    this slot.  
    The particular irq #s that are passed in depend on the routing inside
    your southbridge and on your motherboard.

    -kevinh@ispiri.com
*/
void pci_assign_irqs(unsigned bus, unsigned slot,
	const unsigned char pIntAtoD[4])
{
	unsigned functNum;
	device_t pdev;
	unsigned char line;
	unsigned char irq;
	unsigned char readback;

	/* Each slot may contain up to eight functions */
	for (functNum = 0; functNum < 8; functNum++) {
		pdev = dev_find_slot(bus, (slot << 3) + functNum);

		if (pdev) {
		  line = pci_read_config8(pdev, PCI_INTERRUPT_PIN);

			// PCI spec says all other values are reserved 
			if ((line >= 1) && (line <= 4)) {
				irq = pIntAtoD[line - 1];

				printk_debug("Assigning IRQ %d to %d:%x.%d\n", \
					irq, bus, slot, functNum);

				pci_write_config8(pdev, PCI_INTERRUPT_LINE,\
					pIntAtoD[line - 1]);

				readback = pci_read_config8(pdev, PCI_INTERRUPT_LINE);
				printk_debug("  Readback = %d\n", readback);

				// Change to level triggered
				pci_level_irq(pIntAtoD[line - 1]);
			}
		}
	}
}