xorg fbdev support for < 8 bits per pixel

Dushara Jayasinghe dushara.jayasinghe at hydrix.com
Sun May 15 19:06:15 PDT 2011

On 13/05/2011 9:31 AM, Dushara Jayasinghe wrote:
> On 12/05/2011 11:31 PM, Jonathan Morton wrote:
>> On Thu, 2011-05-12 at 17:58 +1000, Dushara Jayasinghe wrote:
>>> Anyway, just would like to find out, how much effort it would take to
>>> add support for devices with 1/2 bits/pixel depth. I noticed that the
>>> current xorg-fbdev implementation doesn't support these depths.
>>> Just to add context to the question, I'm working on an embedded device
>>> with a monochrome LCD. The CPU can generate grayscale images by upping
>>> the frame-rate and modulating the pixels but the hardware implementation
>>> limits the max FR so I can only support about 2 bits per pixel depth.
>> Would it be sufficient to use an 8bpp greyscale framebuffer and simply
>> ignore the low-order bits on scanout?
> Thanks for you reply Jonathan.
> Maybe I'm a bit out of my depth (hehe) here, could you elaborate on this
> please? The CPU (iMX.25) LCD peripheral (LCDC module) uses a chunk of
> memory to scan out and the bit depth is determined by the video mode
> used. My understanding is, the X FB drv writes directly to this chunk of
> memory (please correct me if I'm wrong). What step are you referring to
> as scanout?

Just curious. Why is it that whenever I ask for things to be elaborated, 
the thread hits dead end? Am I posting to the wrong list?

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