[PATCH 3.17] drm/msm: Fix fbdev for 16- and 24-bit modes.

[Rob Clark]

On Fri, Oct 17, 2014 at 10:28 AM, Daniel Thompson
<daniel.thompson at linaro.org> wrote:
> Currently forcing the video mode from the kernel command line (for example
> video=HDMI-A-1:1280x720-16 at 60) does not correctly set the number of bits
> per pixel. This is due to a rather aggressive override in
> msm_fbdev_create(). This is a particular problem for Android bring up
> because the software EGL fallbacks don't support 32bpp.
>
> This problem could be trivially fixed by removing the override completely.
> However to avoid regressing commit 96673ecbd7f6 ("drm/msm: default to
> XR24 rather than AR24") this patch continues to override the depth if
> there are 32 bits per pixel.
>
> Change was tested by dd'ing a test image to /dev/fb0 with no video=
> (still 32bpp, DBG() message observed), video=1920x1080-32 at 60 (message
> observed), video=1920x1080-24 at 60 and video=1920x1080-16 at 60 .
>
> Signed-off-by: Daniel Thompson <daniel.thompson at linaro.org>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Rob Clark <robdclark at gmail.com>
> ---
>  drivers/gpu/drm/msm/msm_fbdev.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_fbdev.c b/drivers/gpu/drm/msm/msm_fbdev.c
> index ab5bfd2..ed0171d 100644
> --- a/drivers/gpu/drm/msm/msm_fbdev.c
> +++ b/drivers/gpu/drm/msm/msm_fbdev.c
> @@ -93,8 +93,10 @@ static int msm_fbdev_create(struct drm_fb_helper *helper,
>         uint32_t paddr;
>         int ret, size;
>
> -       sizes->surface_bpp = 32;
> -       sizes->surface_depth = 24;
> +       if (sizes->surface_bpp == 32) {
> +               DBG("forcing surface depth to 24\n");
> +               sizes->surface_depth = 24;
> +       }

Thanks.. we could probably even drop this forcing depth to 24.. from a
quick check in drm_fb_helper_single_fb_probe() the default is 24/32
which should be enough for the "flicker-free" handover from splash
screen to X.

Not really sure why I was forcing the depth/bpp.. I think copy/paste
of a hack from another driver to do video 'underlays' ;-)

BR,
-R

>
>         DBG("create fbdev: %dx%d@%d (%dx%d)", sizes->surface_width,
>                         sizes->surface_height, sizes->surface_bpp,
> --
> 1.9.3
>