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

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Date:	Sun, 06 Sep 2015 16:20:39 +0800
From:	Yakir Yang <ykk@...k-chips.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Heiko Stuebner <heiko@...ech.de>,
	Thierry Reding <treding@...dia.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Inki Dae <inki.dae@...sung.com>, Joe Perches <joe@...ches.com>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Mark Yao <mark.yao@...k-chips.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	djkurtz@...omium.com, dianders@...omium.com, seanpaul@...omium.com,
	Ajay kumar <ajaynumb@...il.com>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	David Airlie <airlied@...ux.ie>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Andy Yan <andy.yan@...k-chips.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Kishon Vijay Abraham I <kishon@...com>,
	architt@...eaurora.org,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	linux-rockchip@...ts.infradead.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 14/16] drm: bridge: analogix/dp: try force hpd after
 plug in lookup failed

Hi Rob,

在 09/05/2015 05:46 AM, Rob Herring 写道:
> On Wed, Sep 2, 2015 at 11:27 PM, Yakir Yang <ykk@...k-chips.com> wrote:
>> Hi Rob,
>>
>> 在 09/03/2015 04:17 AM, Rob Herring 写道:
>>> On Tue, Sep 1, 2015 at 1:14 AM, Yakir Yang <ykk@...k-chips.com> 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
> driver.
>
>> 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
>>> DT?
>>
>> 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

> Rob
>
>
>


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