linux-kernel - Re: [PATCH 2/2] video:omapdrm: make omapdrm assume the tv-out cable is always connected

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Date:	Fri, 13 Nov 2015 14:31:48 +0100
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>,
	David Airlie <airlied@...ux.ie>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-fbdev@...r.kernel.org,
	gta04-owner@...delico.com, notasas@...il.com
Subject: Re: [PATCH 2/2] video:omapdrm: make omapdrm assume the tv-out cable is always connected

Hi Laurent and Tomi,

Am 13.11.2015 um 13:01 schrieb Laurent Pinchart <laurent.pinchart@...asonboard.com>:

> On Friday 13 November 2015 13:46:01 Tomi Valkeinen wrote:
>> On 13/11/15 12:29, H. Nikolaus Schaller wrote:
>>> Include VENC in the set of drivers where it is assimed that the cable
>>> is always connected. Like DPI, DSI, DBI and SDI do.
>>> 
>>> Otherwise, the VENC will return cable status "unknown" and is not enabled
>>> by the X-server. So there is no video output signal.
>>> 
>>> Tested on: BeagleBoard XM, GTA04 and OpenPandora
>>> 
>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>> ---
>>> 
>>> drivers/gpu/drm/omapdrm/omap_connector.c | 1 +
>>> 1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/drivers/gpu/drm/omapdrm/omap_connector.c
>>> b/drivers/gpu/drm/omapdrm/omap_connector.c index 83f2a91..98ddb5d 100644
>>> --- a/drivers/gpu/drm/omapdrm/omap_connector.c
>>> +++ b/drivers/gpu/drm/omapdrm/omap_connector.c
>>> @@ -120,6 +120,7 @@ static enum drm_connector_status
>>> omap_connector_detect(
>>> 		else
>>> 			ret = connector_status_disconnected;
>>> 	} else if (dssdev->type == OMAP_DISPLAY_TYPE_DPI ||
>>> +			dssdev->type == OMAP_DISPLAY_TYPE_VENC ||
>>> 			dssdev->type == OMAP_DISPLAY_TYPE_DBI ||
>>> 			dssdev->type == OMAP_DISPLAY_TYPE_SDI ||
>>> 			dssdev->type == OMAP_DISPLAY_TYPE_DSI) {
>> 
>> I have no idea why VENC is not working for you when using
>> connector_status_unknown,

I agree that it should...

>> but I just tested DPI with
>> connector_status_unknown (i.e. changed the above func to return unknown
>> for DPI

Good hint. I can do the same check. Maybe it highlights the real issue.

>> ), and it works fine with X and X omap driver. And xrandr
>> confirms that the connection status is unknown:
>> 
>> # xrandr
>> Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 2048 x 2048
>> HDMI-1 disconnected (normal left inverted right x axis y axis)
>> None-1 unknown connection 1920x1200+0+0 (normal left inverted right x
>> axis y axis) 0mm x 0mm
>>   1920x1200     60.00*+  60.00 +

Which configs, drivers and system are you using for this results?

>> 
>> Grep also shows that there are many drivers using
>> connector_status_unknown, so I'm guessing it should work fine...
> 
> And beside it's not right to consider VENC as always connected, as it isn't. 

Hm. Well, the VENC (meaning the D/A converter inside the OMAP3 chip)
is always connected. But the monitor or cable isn't.

> The unknown status is there for a reason, to describe connectors for which we 
> can't get any status information. The situation is different for DPI, DBI, SDI 
> and DSI as those are on-board busses that connect to a non-removable panel, so 
> we can say with a good confidence that the panel is connected (the situation 
> could be changed with a hammer and a chisel, but that's unlikely to happen, 
> hence the confidence).

Well, it may be that the omapdrm and X11 combination (unfortuantely I don't
understand either and have not found a good description how they interwork),
 keeps the VENC disabled if the connector is unknown.

And since there is no code to detect that a cable has been connected, there
might be missing some trigger to enable the interface.

The symptom I see is that the status of this card is "disabled" while the LCD
panel is "enabled". After doing my proposed patch, both come up "enabled".

So my patch appears to be a work around some other still hidden problem.

Any hint from the experts how to debug / find the real issue & solution is welcome.

BR,
Nikolaus

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