Re: [PATCH v4 14/16] drm: bridge: analogix/dp: try force hpd after plug in lookup failed

From: Yakir Yang
Date: Sun Sep 06 2015 - 04:22:04 EST

Hi Rob,

å 09/05/2015 05:46 AM, Rob Herring åé:
On Wed, Sep 2, 2015 at 11:27 PM, Yakir Yang <ykk@xxxxxxxxxxxxxx> wrote:
Hi Rob,

å 09/03/2015 04:17 AM, Rob Herring åé:
On Tue, Sep 1, 2015 at 1:14 AM, Yakir Yang <ykk@xxxxxxxxxxxxxx> wrote:
Some edp screen do not have hpd signal, so we can't just return
failed when hpd plug in detect failed.
This is a property of the panel (or connector perhaps), so this
property should be located there. At least, it is a common issue and
not specific to this chip. We could have an HDMI connector and failed
to hook up HPD for example. A connector node is also where hpd-gpios
should be located instead (and are already defined by
../bindings/video/hdmi-connector.txt). Perhaps we need a eDP connector
binding, too.

Yep, I agree with your front point, it is a property of panel, not specific
to eDP controller, so this code should handle in connector logic.

But another question, if we just leave this property to connector,
then we would need to parse this property in analogix_dp-rockchip.c,
and then make an hook in analogix_dp_core.c driver. This is not nice,
and if there are some coming platform which alse want to use analogix_dp
code and meet this "no-hpd" situation, then they would need duplicate
to parse this property and fill the hook in analogix_dp_core.c driver.
So it's little bit conflict :-)
Ideally, you would be able to just retrieve this quirk from the
connector or panel. Getting this property from your node vs. the port
you are attached to should not be much harder. Either the connector
struct can have this info or there can be a DT function that can walk
the graph and get it. Just don't open code the graph traversal in your

Beside I can not understand your example very well. Do you mean
that there are some HDMI monitor which also do not have HPD
signal (just like some eDP panel do not have hpd too), and then
the "hpd-gpios" ? Hmm... I don't know how the "hpd-gpios" want
to help in this case, would you mind show some sample code :-D
I don't know that there is h/w, but it is always possible HPD is not
hooked up or hooked up incorrectly some how.

If there is no HPD support, then hpd-gpios is not going to help you.

I think there are 3 cases to handle:
- HPD handled by bridge chip - The bridge driver knows it has this
capability. No DT properties are needed and no HPD properties on the
connector node imply the bridge chip should handle HPD functions.
- HPD handled by GPIO line (or some other block) - Indicated by
hpd-gpios present
- No or broken HPD - Indicated by "hpd-force" property.

Oh, I think the first/second case isn't suitable in this case, my panel
"cnm,n116bgeea2" haven't included HPD signal.

Are there any eDP panels which don't have EDID and need panel details in

Oh, I think you want to collect some info that belong to panel
property but no indicate in panel EDID message, so those can
be collect in eDP connector binding, is it right ?
Yes, and as Thierry pointed out we may need to know the exact panel even.

Yeah, just like I reply to Thierry, this is a panel quirk. And he suggest we should
handle this in panel driver, but I have no idea how to handle this in common panel
driver. :)

- Yakir


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