mx6 hdmi resolution behaviour

Russell King - ARM Linux linux at
Tue Jun 23 13:58:37 PDT 2015

On Tue, Jun 23, 2015 at 05:48:51PM -0300, Fabio Estevam wrote:
> On Tue, Jun 23, 2015 at 5:41 PM, Russell King - ARM Linux
> <linux at> wrote:
> > I've just tried this (the HBi1 was booted previously with the HDMI socket
> > disconnected).  Just now, I turned the TV on, and then connected it to
> > the HDMI.
> Thanks for testing it.
> > The TV reported a resolution of 1024x768, and the kernel log was silent.
> That's the point that makes me confused: shouldn't it report a higher
> resolution like 1080p?

No - it won't go higher than the initial mode that was set.  See

        max_width = fb_helper->fb->width;
        max_height = fb_helper->fb->height;

        drm_fb_helper_probe_connector_modes(fb_helper, max_width, max_height);

This calls connector->funcs->fill_modes with the max width/height,
which calls down into drm_helper_probe_single_connector_modes_merge_bits()
and there's limitations in there which means that we won't try to
increase the size of the framebuffer.

You do get that behaviour if you have the X server running, and that's
all down to the X server itself doing that (reacting to the hotplug
event which DRM generates.)

FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to

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