Re: [PATCH] amba-clcd: add RGB444 support

[Luotao Fu <l.fu@pengutronix.de>]

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Hi Russell,

On Mon, Mar 15, 2010 at 01:38:10PM +0000, Russell King - ARM Linux wrote:
> On Mon, Mar 15, 2010 at 02:30:09PM +0100, Luotao Fu wrote:
> > This one adds RGB444 (bpp=12) support to amba clcd drivers. Tested on a lpc3250
> > based platform.
> 
> No - this is wrong.  You have a 16bpp display.  bpp is the number of bits
> in the framebuffer between two successive pixels.  It is not the number of
> bits used for the pixel information.
> 

> The only case where you have a 12bpp display is if you have two pixels
> packed into three bytes.
>
For 12bpp actually 16bits/pixel is used. I'm aware of that. That's the
reason why the fb.var.bits_per_pixel is set to 16 in clcdfb_decode if
it is originally set to 12 from the platform file to make usage of 16bpp
display. omapfb driver does quite the same.

On my framebuffer controller (here on a lpc3250) there is hardware RGB444
support. Switching to this mode will spare some pins. What I intend to
do with this patch is to make use of this feature. Similar RGB444
Support can be found in omapfb.

cheers
Luotao Fu
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