linux/Documentation/fb/ep93xx-fb.rst
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   1================================
   2Driver for EP93xx LCD controller
   3================================
   4
   5The EP93xx LCD controller can drive both standard desktop monitors and
   6embedded LCD displays. If you have a standard desktop monitor then you
   7can use the standard Linux video mode database. In your board file::
   8
   9        static struct ep93xxfb_mach_info some_board_fb_info = {
  10                .num_modes      = EP93XXFB_USE_MODEDB,
  11                .bpp            = 16,
  12        };
  13
  14If you have an embedded LCD display then you need to define a video
  15mode for it as follows::
  16
  17        static struct fb_videomode some_board_video_modes[] = {
  18                {
  19                        .name           = "some_lcd_name",
  20                        /* Pixel clock, porches, etc */
  21                },
  22        };
  23
  24Note that the pixel clock value is in pico-seconds. You can use the
  25KHZ2PICOS macro to convert the pixel clock value. Most other values
  26are in pixel clocks. See Documentation/fb/framebuffer.rst for further
  27details.
  28
  29The ep93xxfb_mach_info structure for your board should look like the
  30following::
  31
  32        static struct ep93xxfb_mach_info some_board_fb_info = {
  33                .num_modes      = ARRAY_SIZE(some_board_video_modes),
  34                .modes          = some_board_video_modes,
  35                .default_mode   = &some_board_video_modes[0],
  36                .bpp            = 16,
  37        };
  38
  39The framebuffer device can be registered by adding the following to
  40your board initialisation function::
  41
  42        ep93xx_register_fb(&some_board_fb_info);
  43
  44=====================
  45Video Attribute Flags
  46=====================
  47
  48The ep93xxfb_mach_info structure has a flags field which can be used
  49to configure the controller. The video attributes flags are fully
  50documented in section 7 of the EP93xx users' guide. The following
  51flags are available:
  52
  53=============================== ==========================================
  54EP93XXFB_PCLK_FALLING           Clock data on the falling edge of the
  55                                pixel clock. The default is to clock
  56                                data on the rising edge.
  57
  58EP93XXFB_SYNC_BLANK_HIGH        Blank signal is active high. By
  59                                default the blank signal is active low.
  60
  61EP93XXFB_SYNC_HORIZ_HIGH        Horizontal sync is active high. By
  62                                default the horizontal sync is active low.
  63
  64EP93XXFB_SYNC_VERT_HIGH         Vertical sync is active high. By
  65                                default the vertical sync is active high.
  66=============================== ==========================================
  67
  68The physical address of the framebuffer can be controlled using the
  69following flags:
  70
  71=============================== ======================================
  72EP93XXFB_USE_SDCSN0             Use SDCSn[0] for the framebuffer. This
  73                                is the default setting.
  74
  75EP93XXFB_USE_SDCSN1             Use SDCSn[1] for the framebuffer.
  76
  77EP93XXFB_USE_SDCSN2             Use SDCSn[2] for the framebuffer.
  78
  79EP93XXFB_USE_SDCSN3             Use SDCSn[3] for the framebuffer.
  80=============================== ======================================
  81
  82==================
  83Platform callbacks
  84==================
  85
  86The EP93xx framebuffer driver supports three optional platform
  87callbacks: setup, teardown and blank. The setup and teardown functions
  88are called when the framebuffer driver is installed and removed
  89respectively. The blank function is called whenever the display is
  90blanked or unblanked.
  91
  92The setup and teardown devices pass the platform_device structure as
  93an argument. The fb_info and ep93xxfb_mach_info structures can be
  94obtained as follows::
  95
  96        static int some_board_fb_setup(struct platform_device *pdev)
  97        {
  98                struct ep93xxfb_mach_info *mach_info = pdev->dev.platform_data;
  99                struct fb_info *fb_info = platform_get_drvdata(pdev);
 100
 101                /* Board specific framebuffer setup */
 102        }
 103
 104======================
 105Setting the video mode
 106======================
 107
 108The video mode is set using the following syntax::
 109
 110        video=XRESxYRES[-BPP][@REFRESH]
 111
 112If the EP93xx video driver is built-in then the video mode is set on
 113the Linux kernel command line, for example::
 114
 115        video=ep93xx-fb:800x600-16@60
 116
 117If the EP93xx video driver is built as a module then the video mode is
 118set when the module is installed::
 119
 120        modprobe ep93xx-fb video=320x240
 121
 122==============
 123Screenpage bug
 124==============
 125
 126At least on the EP9315 there is a silicon bug which causes bit 27 of
 127the VIDSCRNPAGE (framebuffer physical offset) to be tied low. There is
 128an unofficial errata for this bug at::
 129
 130        https://marc.info/?l=linux-arm-kernel&m=110061245502000&w=2
 131
 132By default the EP93xx framebuffer driver checks if the allocated physical
 133address has bit 27 set. If it does, then the memory is freed and an
 134error is returned. The check can be disabled by adding the following
 135option when loading the driver::
 136
 137      ep93xx-fb.check_screenpage_bug=0
 138
 139In some cases it may be possible to reconfigure your SDRAM layout to
 140avoid this bug. See section 13 of the EP93xx users' guide for details.
 141