[PATCH 09/26] video: Add support for copying to a hardware framebuffer

[Anatolij Gustschin]

On Tue, 19 May 2020 17:10:41 -0600
Simon Glass sjg at chromium.org wrote:

> Some architectures use a cached framebuffer and flush the cache as needed
> so that changes are visible. This is supported by U-Boot.
> 
> However x86 uses an uncached framebuffer with a 'write-combining' feature
> to speed up writes.  Reads are permitted but they are extremely expensive.
> 
> Unfortunately, reading from the frame buffer is quite common, e.g. to
> scroll it. This makes scrolling very slow.
> 
> Add a new feature which supports copying modified parts of the frame
> buffer to the uncached hardware buffer. This speeds up scrolling by at
> least 10x on x86 so the extra complexity cost seems worth it.
> 
> As a starting point, add the Kconfig, update the video structures to keep
> track of the buffer and add a function to do the copy.
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>

Reviewed-by: Anatolij Gustschin <agust at denx.de>