Re: [PATCH] drm: bridge/dw_hdmi: Filter modes > 165MHz for DVI

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Jun 17, 2015 at 04:14:07PM -0700, Doug Anderson wrote:
> If you plug in a DVI monitor to your HDMI port, you need to filter out
> clocks > 165MHz.  That's because 165MHz is the maximum clock rate that
> we can run single-link DVI at.
> 
> If you want to run high resolutions to DVI, you'd need some type of an
> active adapter that pretended that it was HDMI, interpreted the
> signal, and produced a new dual link DVI signal at a lower clock rate.
> 
> Signed-off-by: Doug Anderson <dianders@chromium.org>
> ---
> Note: this patch was tested against a 3.14 kernel with backports.  It
> was only compile tested against linuxnext, but the code is
> sufficiently similar that I'm convinced it will work there.

Really?  I have to wonder what your testing was...

        hdmi->vic = drm_match_cea_mode(mode);

        if (!hdmi->vic) {
                dev_dbg(hdmi->dev, "Non-CEA mode used in HDMI\n");
                hdmi->hdmi_data.video_mode.mdvi = true;
        } else {
                dev_dbg(hdmi->dev, "CEA mode used vic=%d\n", hdmi->vic);
                hdmi->hdmi_data.video_mode.mdvi = false;
        }

mdvi indicates whether the _currently set mode_ is a CEA mode or not (imho,
it's mis-named).  It doesn't indicate whether we have a HDMI display device
or a DVI display device connected, which seems to be what you want to use
it for below.

To sort that, what you need to do is detect a HDMI display device using
drm_detect_hdmi_monitor() on the EDID received from the device before
parsing the modes, and save that value in a dw_hdmi struct member, and
I'd suggest that it's a top-level struct member, not buried in 'hdmi_data'
or 'video_mode'.

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