• Antonino A. Daplas's avatar
    [PATCH] fbcon: Console Rotation - Prepare fbcon for console rotation · e4fc2761
    Antonino A. Daplas authored
    This patch series implements generic code to rotate the console at 90, 180,
    and 270 degrees. The implementation is completely done in the framebuffer
    console level, thus no changes to the framebuffer layer or to the drivers
    are needed.
    
    Console rotation is required by some Sharp-based devices where the natural
    orientation of the display is not at 0 degrees. Also, users that have
    displays that can pivot will benefit by having a console in portrait mode
    if they so desire.
    
    The choice to implement the code in the console layer rather than in the
    framebuffer layer is due to the following reasons:
    
    - it's fast
    - it does not require driver changes
    - it can coexist with devices that can rotate the display at the hardware level
    - it complements graphics applications that can do display rotation
    
    The changes to core fbcon are minimal-- recognition of the console
    rotation angle so it can swap directions, origins and axes (xres vs yres,
    xpanstep vs ypanstep, xoffset vs yoffset, etc) and storage of the rotation
    angle per display. The bulk of the code that does the actual drawing to the
    screen are placed in separate files. Each angle of rotation has separate
    methods (bmove, clear, putcs, cursor, update_start which is derived from
    update_var, and clear_margins).  To mimimize processing time, the fontdata
    are pre-rotated at each console switch (only if the font or the angle has
    changed).
    
    The option can be compiled out (CONFIG_FRAMEBUFFER_CONSOLE_ROTATION = n) if
    rotation is not needed.
    
    Choosing the rotation angle can be done in several ways:
    
    1. boot option fbcon=rotate:n, where
         n = 0 - normal
         n = 1 - 90 degrees (clockwise)
         n = 2 - 180 degrees (upside down)
         n = 3 - 270 degrees (counterclockwise)
    
    2. echo n > /sys/class/graphics/fb[num]/con_rotate
    
         where n is the same as described above. It sets the angle of rotation
    of the current console
    
    3 echo n > /sys/class/graphics/fb[num]/con_rotate_all
    
         where n is the same as described above. Globally sets the angle of
    rotation.
    
    GOTCHAS:
    
    	The option, especially at angles of 90 and 270 degrees, will exercise
    the least used code of drivers.  Namely, at these angles, panning is done
    in the x-axis, so it can reveal bugs in the driver if xpanstep is set
    incorrectly. A workaround is to set xpanstep = 0.
    
    	Secondly, at these angles, the framebuffer memory access can be
    unaligned if (fontheight * bpp) % 32 ~= 0 which can reveal bugs in the drivers
    imageblit, fillrect and copyarea functions.  (I think cfbfillrect may have
    this buglet). A workaround is to use a standard 8x16 font.
    
    Speed:
    
    	The scrolling speed difference between 0 and 180 degrees is minimal,
    somewhere areound 1-2%.  At 90 or 270 degress, speed drops down to a vicinity
    of 30-40%. This is understandable because the blit direction is across the
    framebuffer "direction." Scrolling will be helped at these angles if xpanstep
    is not equal to zero, use of 8x16 fonts, and setting xres_virtual >= xres * 2.
    
    Note: The code is tested on little-endian only, so I don't know if it will
    work in big-endian. Please let me know, it will take only less than a minute
    of your time.
    
    This patch prepares fbcon for console rotation and contains the following
    changes:
    
    - add rotate field in struct fbcon_ops to keep fbcon's current rotation
      angle
    
    - add con_rotate field in struct display to store per-display rotation angle
    
    - create a private copy of the current var to fbcon.  This will prevent
      fbcon from directly manipulating info->var, especially the fields xoffset,
      yoffset and vmode.
    
    - add ability to swap pertinent axes (xres, yres; xpanstep, ypanstep; etc)
      depending on the rotation angle
    
    - change global update_var() (function that sets the screen start address)
      as an fbcon method update_start.  This is required because the axes, start
      offset, and/or direction can be reversed depending on the rotation angle.
    
    - add fbcon method rotate_font() which will rotate each character bitmap to
      the correct angle of rotation.
    
    - add fbcon boot option 'rotate' to select the angle of rotation at bootime.
       Currently does nothing until all patches are applied.
    Signed-off-by: default avatarAntonino Daplas <adaplas@pol.net>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    e4fc2761
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