[PATCH v5 4/8] drm/cma-helper: Use the generic fbdev emulation

[Laurent Pinchart]

Hi John,

On Thursday, 23 August 2018 07:14:08 EEST John Stultz wrote:
> On Mon, Aug 20, 2018 at 11:44 PM, John Stultz wrote:
> > Hey Noralf, all,
> > 
> >   I've been digging for a bit on the regression that this patch has
> > 
> > tripped on the HiKey board as reported here:
> > https://lkml.org/lkml/2018/8/16/81
> > 
> > The first issue was that the kirin driver was setting
> > mode_config.max_width/height = 2048, which was causing errors as the
> > the requested resolution was 1920x2160 (due to surfaceflinger
> > requesting y*2 for page flipping).
> 
> Hey Noralf,
>   Sorry, I know your probably sick of me. But I just wanted to circle
> around on this little bit. So part of the issue I found earlier, was
> that I'm running w/ CONFIG_DRM_FBDEV_OVERALLOC=200, to support
> Surfaceflinger's request for page flipping.

Possibly slightly out of topic, but we're in 2018, is there any plan to make 
SurfaceFlinger move away from FBDEV ?

> This is what makes the Y resolution 2160, which runs afoul of the new
> max_height check of 2048 in the generic code.
> 
> I was checking with Xinliang, who know the kirin display hardware,
> about the max_height being set to 2048 to ensure bumping it up wasn't
> a problem, but he said 2048x2048  was unfortunately not arbitrary, and
> that was the hard limit of the display hardware. However, with
> overalloc, the 1920x2160 res fbdev should still be ok, as only
> 1920x1080 is actually displayed at one time.
> 
> So it seems like we might need to multiply the max_height by the
> overalloc factor when we are checking it in
> drm_internal_framebuffer_create?
> 
> Does that approach sound sane, or would folks prefer something different?

-- 
Regards,

Laurent Pinchart