//-------------------------------------------------------------------
//	mysis.c
//
//	programmer: ALLAN CRUSE
//	written on: 22 APR 2003
//	revised on: 25 APR 2003 -- to correct and clarify 'mmap()'
//-------------------------------------------------------------------

#define	__KERNEL__
#define	  MODULE  

#include <linux/module.h>	// for init_module() 
#include <linux/pci.h>		// for pci_find_class()
#include <linux/mm.h>		// for remap_page_range()

#define	VGA_CLASS 0x030000	// for VGA Display Adapters

static char modname[] = "mysis";
static char devname[] = "/dev/vram";
static int my_major = 99;	// driver's assigned major number
static unsigned long fb_base;	// physical address of frame buffer
static unsigned long fb_size;	// size of the frame buffer (bytes)

static int my_mmap( struct file *file, struct vm_area_struct *vma )
{
	unsigned long	region_length = vma->vm_end - vma->vm_start;
	unsigned long	region_origin = vma->vm_pgoff * PAGE_SIZE;
	unsigned long	phys_addr = fb_base + region_origin;
	unsigned long	virt_addr = vma->vm_start;
	
	// cannot map a file-region that extends past end-of-file
	if ( region_origin + region_length > fb_size ) return -EINVAL;

	// tell kernel not to try swapping out this device-memory
	vma->vm_flags |= VM_RESERVED;

	// request the kernel to set up the necessary page-tables
	if ( remap_page_range( virt_addr, phys_addr, region_length, 
				vma->vm_page_prot ) ) return -EAGAIN;
	return	0; // SUCCESS;
}

static loff_t my_llseek( struct file *file, loff_t offset, int whence )
{
	loff_t	newpos = -1;
	switch( whence )
		{
		case 0:	newpos = offset; break;			// SEEK_SET
		case 1:	newpos = file->f_pos + offset; break;	// SEEK_CUR
		case 2:	newpos = fb_size + offset; break;	// SEEK_END
		}
	if (( newpos < 0 )||( newpos > fb_base )) return -EINVAL;
	file->f_pos = newpos;
	return	newpos;
}



static struct file_operations 
my_fops =	{
		owner:		THIS_MODULE,
		llseek:		my_llseek,
		mmap:		my_mmap,		
		};



int init_module( void )
{
	struct	pci_dev	*devp = NULL;
	u32	save, temp;
	int	i;
	
	printk( "<1>\nInstalling \'%s\' module ", modname );
	printk( "(major=%d) \n", my_major );
	
	devp = pci_find_class( VGA_CLASS, devp );
	if ( !devp ) return -ENODEV;

	fb_base = pci_resource_start( devp, 0 );

	temp = ~0;
	pci_read_config_dword( devp, 0x10, &save );
	pci_write_config_dword( devp, 0x10, temp );
	pci_read_config_dword( devp, 0x10, &temp );
	pci_write_config_dword( devp, 0x10, save );
	for (i = 4; i < 32; i++) if ( temp & (1<<i) ) break;
	fb_size = (1<<i);
	
	printk( "<1>  VGA Device: %s \n", devp->name );
	printk( "<1>  frame-buffer starts at %08X ", fb_base );
	printk( "(%d MB)\n", fb_size >> 20 );
	
	return	register_chrdev( my_major, modname, &my_fops );
}


void cleanup_module( void )
{
	unregister_chrdev( my_major, modname );

	printk( "<1>Removing \'%s\' module\n", modname );
}

MODULE_LICENSE("GPL");

// Thanks to Qing Huang for pointing out a flaw in 'mmap()' earlier.