• Jaya Kumar's avatar
    broadsheetfb: support storing waveform · b32bfc38
    Jaya Kumar authored
    This patch adds waveform storing capability to broadsheetfb. It uses the
    firmware class to retrieve the waveform, and the request to initiate the
    waveform storing is done via a driver sysfs entry, loadstore_waveform.
    
    Broadsheet is a framebuffer device.  It is slightly different from a
    typical framebuffer controller that drives a normal TFT-LCD display.  Most
    E-Ink display panels require a waveform in order to function.  That is, in
    order to drive the state of a pixel to black, gray, or white, a specific
    waveform is utilized.  Basically, that waveform represents the specific
    E-field wiggling needed to get the pixel to its optimal state given
    current temperature, and its previous state.  TN/IPS-LCDs use a similar
    concept but the driving waveform is sufficiently simple that it is
    internalized in the TFT source/gate driver.
    
    These E-Ink waveforms are specific to a production batch.  That is, a
    batch of display films are produced, then they get characterized and a
    waveform is generated for that batch.  Broadsheet, typically, is attached
    to its private SPI flash which is then flashed with this waveform.
    
    Users won't be able to see the waveform and typically won't ever need to
    know about it.  If however, the display panel attached to broadsheet is
    changed out, then they will need to update their waveform.  That would
    typically be done at a factory or repair facility rather than by a user.
    
    [akpm@linux-foundation.org: fix printk warning]
    Signed-off-by: default avatarJaya Kumar <jayakumar.lkml@gmail.com>
    Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    b32bfc38
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