cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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ep93xx-fb.rst (4576B)


      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.