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141 lines
4.5 KiB
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141 lines
4.5 KiB
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================================
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Driver for EP93xx LCD controller
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================================
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The EP93xx LCD controller can drive both standard desktop monitors and
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embedded LCD displays. If you have a standard desktop monitor then you
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can use the standard Linux video mode database. In your board file::
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static struct ep93xxfb_mach_info some_board_fb_info = {
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.num_modes = EP93XXFB_USE_MODEDB,
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.bpp = 16,
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};
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If you have an embedded LCD display then you need to define a video
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mode for it as follows::
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static struct fb_videomode some_board_video_modes[] = {
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{
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.name = "some_lcd_name",
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/* Pixel clock, porches, etc */
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},
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};
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Note that the pixel clock value is in pico-seconds. You can use the
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KHZ2PICOS macro to convert the pixel clock value. Most other values
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are in pixel clocks. See Documentation/fb/framebuffer.rst for further
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details.
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The ep93xxfb_mach_info structure for your board should look like the
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following::
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static struct ep93xxfb_mach_info some_board_fb_info = {
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.num_modes = ARRAY_SIZE(some_board_video_modes),
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.modes = some_board_video_modes,
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.default_mode = &some_board_video_modes[0],
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.bpp = 16,
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};
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The framebuffer device can be registered by adding the following to
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your board initialisation function::
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ep93xx_register_fb(&some_board_fb_info);
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=====================
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Video Attribute Flags
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=====================
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The ep93xxfb_mach_info structure has a flags field which can be used
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to configure the controller. The video attributes flags are fully
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documented in section 7 of the EP93xx users' guide. The following
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flags are available:
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=============================== ==========================================
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EP93XXFB_PCLK_FALLING Clock data on the falling edge of the
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pixel clock. The default is to clock
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data on the rising edge.
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EP93XXFB_SYNC_BLANK_HIGH Blank signal is active high. By
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default the blank signal is active low.
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EP93XXFB_SYNC_HORIZ_HIGH Horizontal sync is active high. By
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default the horizontal sync is active low.
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EP93XXFB_SYNC_VERT_HIGH Vertical sync is active high. By
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default the vertical sync is active high.
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=============================== ==========================================
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The physical address of the framebuffer can be controlled using the
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following flags:
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=============================== ======================================
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EP93XXFB_USE_SDCSN0 Use SDCSn[0] for the framebuffer. This
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is the default setting.
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EP93XXFB_USE_SDCSN1 Use SDCSn[1] for the framebuffer.
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EP93XXFB_USE_SDCSN2 Use SDCSn[2] for the framebuffer.
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EP93XXFB_USE_SDCSN3 Use SDCSn[3] for the framebuffer.
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=============================== ======================================
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==================
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Platform callbacks
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==================
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The EP93xx framebuffer driver supports three optional platform
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callbacks: setup, teardown and blank. The setup and teardown functions
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are called when the framebuffer driver is installed and removed
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respectively. The blank function is called whenever the display is
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blanked or unblanked.
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The setup and teardown devices pass the platform_device structure as
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an argument. The fb_info and ep93xxfb_mach_info structures can be
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obtained as follows::
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static int some_board_fb_setup(struct platform_device *pdev)
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{
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struct ep93xxfb_mach_info *mach_info = pdev->dev.platform_data;
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struct fb_info *fb_info = platform_get_drvdata(pdev);
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/* Board specific framebuffer setup */
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}
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======================
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Setting the video mode
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======================
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The video mode is set using the following syntax::
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video=XRESxYRES[-BPP][@REFRESH]
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If the EP93xx video driver is built-in then the video mode is set on
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the Linux kernel command line, for example::
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video=ep93xx-fb:800x600-16@60
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If the EP93xx video driver is built as a module then the video mode is
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set when the module is installed::
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modprobe ep93xx-fb video=320x240
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==============
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Screenpage bug
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==============
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At least on the EP9315 there is a silicon bug which causes bit 27 of
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the VIDSCRNPAGE (framebuffer physical offset) to be tied low. There is
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an unofficial errata for this bug at::
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http://marc.info/?l=linux-arm-kernel&m=110061245502000&w=2
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By default the EP93xx framebuffer driver checks if the allocated physical
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address has bit 27 set. If it does, then the memory is freed and an
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error is returned. The check can be disabled by adding the following
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option when loading the driver::
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ep93xx-fb.check_screenpage_bug=0
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In some cases it may be possible to reconfigure your SDRAM layout to
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avoid this bug. See section 13 of the EP93xx users' guide for details.
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