linux-kernel - Re: [BISECTED, REGRESSION] v4.12-rc: omapdrm fails to probe on Nokia N900

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Date:   Fri, 30 Jun 2017 12:02:48 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Aaro Koskinen <aaro.koskinen@....fi>
CC:     Peter Ujfalusi <peter.ujfalusi@...com>,
        Tony Lindgren <tony@...mide.com>,
        <linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [BISECTED, REGRESSION] v4.12-rc: omapdrm fails to probe on Nokia
 N900

On 30/06/17 11:58, Aaro Koskinen wrote:
> Hi,
> 
> On Fri, Jun 30, 2017 at 09:41:35AM +0300, Tomi Valkeinen wrote:
>> On 29/06/17 21:50, Aaro Koskinen wrote:
>>> On Thu, Jun 15, 2017 at 09:51:06AM +0300, Tomi Valkeinen wrote:
>>>> On 15/06/17 01:11, Aaro Koskinen wrote:
>>>>> When booting v4.12-rc5 on Nokia N900, omapdrm fails to probe and there
>>>>> is no display.
>>>>
>>>> Are you sure it doesn't probe? It fails the omapdss_stack_is_ready()
>>>> check?
>>>
>>> It appears the reason was that I didn't have
>>> CONFIG_DRM_OMAP_CONNECTOR_ANALOG_TV enabled.
>>>
>>> I think that's wrong. I don't own an analog TV, so why should I enable
>>> such option to get device's built-in display working?
>>
>> Indeed. Unfortunately I don't have a solution for that.
>>
>> DRM doesn't support adding devices after probe. So at omapdrm probe time
>> we have to decide which displays to use. In the dts file, n900 defines
>> the lcd and analog tv. omapdrm sees those, and, of course, must wait
>> until their respective drivers have probed. If you don't have the
>> display driver enabled, it's never loaded and omapdrm never probes as it
>> keeps waiting for those.
> 
> Could you at least print some kind of message early in the boot ("omapdrm
> is waiting for drivers for display x and y")?

That could be quite spammy. omapdrm will defer probe if the displays are
not present, and the deferred probing machinery will then cause a new
omapdrm probe later. That can happen a lot of times before the drivers
are there.

 Tomi



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