[Intel-gfx] [PATCH] drm/i915: Add support to change pixel format, tiling mode, tiling offset.

[Chris Wilson]

On Mon, Sep 23, 2013 at 11:32:40AM +0000, Ramakutty, SandeepX wrote:
> Hi Chris,
> 
> This patch is necessary for applying pixel format changes without creating new frame buffer.

No, it doesn't. As pixelformat is only specified with AddFB2, it appears
there is something else required to allow changing format on an existing
fb on the fly.

> The pixel format will be changed at page flip.  
> Background - The present kernel code does not support applying pixel format to the current frame buffer. Hence hardware composer needs to create a new frame buffer each time it needs to change the frame buffer.  If the application/game tries to change the pixel format very frequently, this affects performance.  
> Motivation - This change enables the hardware composer to apply the new pixel format without creating  a new framebuffer. This improves the performance at a time when the application frequently changes the pixel format.

That's obvious from the patch. I was hoping for more details on the use
case to demonstrate the necessity of this approach, I still do not see
a scenario that would require frequent changes in scanout pixelformat.

Quantify, quantify, quantify. Then we know whether the approach meets
your goal, and more importantly detect any future regressions.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre