[PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

Hi,

On Thu, Feb 16, 2017 at 01:28:24PM +0100, Tobias Jakobi wrote:
> Hello,
> 
> I'm not sure if I'm missing something here, but I don't see how this is
> supposed to work.
> 
> This just multiplies the height of the drm_mode_fb_cmd2 object with the
> number of buffers. Let's say I have width=1024, height=768, then now I
> have a framebuffer which has height=2304 (in the num_buffers=3 case). At
> some point this FB is set as the primary plane, giving us a 1024x2304
> mode. I don't think that this is intended.
> 
> In my opinion this multi-buffer thing should touch drm_mode_fb_cmd2 at
> all. The underlying BO should be larger, but not the FB itself. If this
> is supposed to work, then the fbdev helpers should create as many FBs as
> there are buffers, and then offset each of these FB into the BO.

This only increases the virtual resolution, not the visible one.

> What I'm also not seeing is code that handles the fbdev's virtual
> resolutions. After all num_buffers should only increase those. Same for
> the panning ioctl().

This is already implemented through drm_fb_helper_pan_display.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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