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

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Message-ID: <1c44c560-a8f3-04e2-9558-1639441e3e32@ti.com>
Date:   Mon, 31 Jul 2017 15:59:43 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Pavel Machek <pavel@....cz>
CC:     Aaro Koskinen <aaro.koskinen@....fi>,
        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 04/07/17 18:09, Pavel Machek wrote:
> Hi!
> 
>>>>>> 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.
> 
> Well doing printk just once should not be a problem...?

I'm not sure if that would really help much... And you would practically
always see the print, even when everything works fine, which would be
useless and could raise false alarms.

 Tomi



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