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

[John Stultz]

On Mon, Aug 20, 2018 at 11:44 PM, John Stultz <john.stultz at linaro.org> 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. 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?

thanks
-john