path: root/drivers/video/skeletonfb.c

/*
 * linux/drivers/video/skeletonfb.c -- Skeleton for a frame buffer device
 *
 *  Modified to new api Jan 2001 by James Simmons (jsimmons@transvirtual.com)
 *
 *  Created 28 Dec 1997 by Geert Uytterhoeven
 *
 *
 *  I have started rewriting this driver as a example of the upcoming new API
 *  The primary goal is to remove the console code from fbdev and place it
 *  into fbcon.c. This reduces the code and makes writing a new fbdev driver
 *  easy since the author doesn't need to worry about console internals. It
 *  also allows the ability to run fbdev without a console/tty system on top 
 *  of it. 
 *
 *  First the roles of struct fb_info and struct display have changed. Struct
 *  display will go away. The way the new framebuffer console code will
 *  work is that it will act to translate data about the tty/console in 
 *  struct vc_data to data in a device independent way in struct fb_info. Then
 *  various functions in struct fb_ops will be called to store the device 
 *  dependent state in the par field in struct fb_info and to change the 
 *  hardware to that state. This allows a very clean separation of the fbdev
 *  layer from the console layer. It also allows one to use fbdev on its own
 *  which is a bounus for embedded devices. The reason this approach works is  
 *  for each framebuffer device when used as a tty/console device is allocated
 *  a set of virtual terminals to it. Only one virtual terminal can be active 
 *  per framebuffer device. We already have all the data we need in struct 
 *  vc_data so why store a bunch of colormaps and other fbdev specific data
 *  per virtual terminal. 
 *
 *  As you can see doing this makes the con parameter pretty much useless
 *  for struct fb_ops functions, as it should be. Also having struct  
 *  fb_var_screeninfo and other data in fb_info pretty much eliminates the 
 *  need for get_fix and get_var. Once all drivers use the fix, var, and cmap
 *  fbcon can be written around these fields. This will also eliminate the
 *  need to regenerate struct fb_var_screeninfo, struct fb_fix_screeninfo
 *  struct fb_cmap every time get_var, get_fix, get_cmap functions are called
 *  as many drivers do now. 
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License. See the file COPYING in the main directory of this archive for
 *  more details.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/fb.h>
#include <linux/init.h>
#include <linux/pci.h>

    /*
     *  This is just simple sample code.
     *
     *  No warranty that it actually compiles.
     *  Even less warranty that it actually works :-)
     */

/*
 * Driver data
 */
static char *mode_option __devinitdata;

/*
 *  If your driver supports multiple boards, you should make the  
 *  below data types arrays, or allocate them dynamically (using kmalloc()). 
 */ 

/* 
 * This structure defines the hardware state of the graphics card. Normally
 * you place this in a header file in linux/include/video. This file usually
 * also includes register information. That allows other driver subsystems
 * and userland applications the ability to use the same header file to 
 * avoid duplicate work and easy porting of software. 
 */
struct xxx_par;

/*
 * Here we define the default structs fb_fix_screeninfo and fb_var_screeninfo
 * if we don't use modedb. If we do use modedb see xxxfb_init how to use it
 * to get a fb_var_screeninfo. Otherwise define a default var as well. 
 */
static struct fb_fix_screeninfo xxxfb_fix __devinitdata = {
	.id =		"FB's name", 
	.type =		FB_TYPE_PACKED_PIXELS,
	.visual =	FB_VISUAL_PSEUDOCOLOR,
	.xpanstep =	1,
	.ypanstep =	1,
	.ywrapstep =	1, 
	.accel =	FB_ACCEL_NONE,
};

    /*
     * 	Modern graphical hardware not only supports pipelines but some 
     *  also support multiple monitors where each display can have its  
     *  its own unique data. In this case each display could be  
     *  represented by a separate framebuffer device thus a separate 
     *  struct fb_info. Now the struct xxx_par represents the graphics
     *  hardware state thus only one exist per card. In this case the 
     *  struct xxx_par for each graphics card would be shared between 
     *  every struct fb_info that represents a framebuffer on that card. 
     *  This allows when one display changes it video resolution (info->var) 
     *  the other displays know instantly. Each display can always be
     *  aware of the entire hardware state that affects it because they share
     *  the same xxx_par struct. The other side of the coin is multiple
     *  graphics cards that pass data around until it is finally displayed
     *  on one monitor. Such examples are the voodoo 1 cards and high end
     *  NUMA graphics servers. For this case we have a bunch of pars, each
     *  one that represents a graphics state, that belong to one struct 
     *  fb_info. Their you would want to have *par point to a array of device
     *  states and have each struct fb_ops function deal with all those 
     *  states. I hope this covers every possible hardware design. If not
     *  feel free to send your ideas at jsimmons@users.sf.net 
     */

    /*
     *  If your driver supports multiple boards or it supports multiple 
     *  framebuffers, you should make these arrays, or allocate them 
     *  dynamically using framebuffer_alloc() and free them with
     *  framebuffer_release().
     */ 
static struct fb_info info;

    /* 
     * Each one represents the state of the hardware. Most hardware have
     * just one hardware state. These here represent the default state(s). 
     */
static struct xxx_par __initdata current_par;

int xxxfb_init(void);

/**
 *	xxxfb_open - Optional function. Called when the framebuffer is
 *		     first accessed.
 *	@info: frame buffer structure that represents a single frame buffer
 *	@user: tell us if the userland (value=1) or the console is accessing
 *	       the framebuffer. 
 *
 *	This function is the first function called in the framebuffer api.
 *	Usually you don't need to provide this function. The case where it 
 *	is used is to change from a text mode hardware state to a graphics
 * 	mode state. 
 *
 *	Returns negative errno on error, or zero on success.
 */
static int xxxfb_open(struct fb_info *info, int user)
{
    return 0;
}

/**
 *	xxxfb_release - Optional function. Called when the framebuffer 
 *			device is closed. 
 *	@info: frame buffer structure that represents a single frame buffer
 *	@user: tell us if the userland (value=1) or the console is accessing
 *	       the framebuffer. 
 *	
 *	Thus function is called when we close /dev/fb or the framebuffer 
 *	console system is released. Usually you don't need this function.
 *	The case where it is usually used is to go from a graphics state
 *	to a text mode state.
 *
 *	Returns negative errno on error, or zero on success.
 */
static int xxxfb_release(struct fb_info *info, int user)
{
    return 0;
}

/**
 *      xxxfb_check_var - Optional function. Validates a var passed in. 
 *      @var: frame buffer variable screen structure
 *      @info: frame buffer structure that represents a single frame buffer 
 *
 *	Checks to see if the hardware supports the state requested by
 *	var passed in. This function does not alter the hardware state!!! 
 *	This means the data stored in struct fb_info and struct xxx_par do 
 *      not change. This includes the var inside of struct fb_info. 
 *	Do NOT change these. This function can be called on its own if we
 *	intent to only test a mode and not actually set it. The stuff in 
 *	modedb.c is a example of this. If the var passed in is slightly 
 *	off by what the hardware can support then we alter the var PASSED in
 *	to what we can do.
 *
 *      For values that are off, this function must round them _up_ to the
 *      next value that is supported by the hardware.  If the value is
 *      greater than the highest value supported by the hardware, then this
 *      function must return -EINVAL.
 *
 *      Exception to the above rule:  Some drivers have a fixed mode, ie,
 *      the hardware is already set at boot up, and cannot be changed.  In
 *      this case, it is more acceptable that this function just return
 *      a copy of the currently working var (info->var). Better is to not
 *      implement this function, as the upper layer will do the copying
 *      of the current var for you.
 *
 *      Note:  This is the only function where the contents of var can be
 *      freely adjusted after the driver has been registered. If you find
 *      that you have code outside of this function that alters the content
 *      of var, then you are doing something wrong.  Note also that the
 *      contents of info->var must be left untouched at all times after
 *      driver registration.
 *
 *	Returns negative errno on error, or zero on success.
 */
static int xxxfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
{
    /* ... */
    return 0;	   	
}

/**
 *      xxxfb_set_par - Optional function. Alters the hardware state.
 *      @info: frame buffer structure that represents a single frame buffer
 *
 *	Using the fb_var_screeninfo in fb_info we set the resolution of the
 *	this particular framebuffer. This function alters the par AND the
 *	fb_fix_screeninfo stored in fb_info. It doesn't not alter var in 
 *	fb_info since we are using that data. This means we depend on the
 *	data in var inside fb_info to be supported by the hardware. 
 *
 *      This function is also used to recover/restore the hardware to a
 *      known working state.
 *
 *	xxxfb_check_var is always called before xxxfb_set_par to ensure that
 *      the contents of var is always valid.
 *
 *	Again if you can't change the resolution you don't need this function.
 *
 *      However, even if your hardware does not support mode changing,
 *      a set_par might be needed to at least initialize the hardware to
 *      a known working state, especially if it came back from another
 *      process that also modifies the same hardware, such as X.
 *
 *      If this is the case, a combination such as the following should work:
 *
 *      static int xxxfb_check_var(struct fb_var_screeninfo *var,
 *                                struct fb_info *info)
 *      {
 *              *var = info->var;
 *              return 0;
 *      }
 *
 *      static int xxxfb_set_par(struct fb_info *info)
 *      {
 *              init your hardware here
 *      }
 *
 *	Returns negative errno on error, or zero on success.
 */
static int xxxfb_set_par(struct fb_info *info)
{
    struct xxx_par *par = info->par;
    /* ... */
    return