linux-kernel - Re: [REGRESSION] omapdrm/N900 display broken

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Date:   Tue, 4 Aug 2020 15:39:37 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Aaro Koskinen <aaro.koskinen@....fi>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Tony Lindgren <tony@...mide.com>, <linux-omap@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] omapdrm/N900 display broken

On 04/08/2020 15:13, Tomi Valkeinen wrote:
> On 28/07/2020 21:14, Aaro Koskinen wrote:
>> Hi,
>>
>> Looks like N900 display support has broken after v5.6.
>>
>> When using v5.7, or the current mainline (v5.8-rc7), the boot hangs at:
>>
>> [    6.269500] omapdss_dss 48050000.dss: 48050000.dss supply vdda_video not found, using dummy regulator
>> [    6.321685] DSS: OMAP DSS rev 2.0
>> [    6.328002] omapdss_dss 48050000.dss: bound 48050400.dispc (ops dispc_component_ops)
>> [    6.336364] omapdss_dss 48050000.dss: bound 48050c00.encoder (ops venc_component_ops)
>> [    6.345153] omapdrm omapdrm.0: DMM not available, disable DMM support
>> [    6.352447] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
>>
>> with a blank display.
>>
>> I tried to bisect this, and the first commit that breaks the display is:
>>
>> 2f004792adadcf017fde50339b432a26039fff0c is the first bad commit
>> commit 2f004792adadcf017fde50339b432a26039fff0c
>> Author: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> Date:   Wed Feb 26 13:24:57 2020 +0200
>>
>>     drm/omap: venc: Register a drm_bridge
>>
>> This commit does not yet hang the kernel, but the display is blank and
>> the probe fails:
>>
>> [    6.290100] omapdss_dss 48050000.dss: 48050000.dss supply vdda_video not foun
>> d, using dummy regulator
>> [    6.342346] DSS: OMAP DSS rev 2.0
>> [    6.348663] omapdss_dss 48050000.dss: bound 48050400.dispc (ops dispc_component_ops)
>> [    6.357025] omapdss_dss 48050000.dss: bound 48050c00.encoder (ops venc_component_ops)
>> [    6.365814] omapdrm omapdrm.0: DMM not available, disable DMM support
>> [    6.372863] omapdrm omapdrm.0: omap_modeset_init failed: ret=-22
>> [    6.414611] omapdrm: probe of omapdrm.0 failed with error -22
> 
> Afaics, this is caused by the patch doing
> 
> 	if (!venc->output.next_bridge)
> 
> instead of
> 
> 	if (venc->output.next_bridge)
> 
> Fixing that removes the error on beagle xm, but for some reason I don't see TV-out as a DRM output
> (but HDMI output works).
> 
>> The hang seems to start with this commit:
>>
>> commit 8bef8a6d5da81b909a190822b96805a47348146f (HEAD -> master)
>> Author: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> Date:   Wed Feb 26 13:25:10 2020 +0200
>>
>>     drm/omap: sdi: Register a drm_bridge
>>
>> Confusingly, some of the commits between these two commits do provide a
>> working display, e.g. 13d2d52f59c0c79398d9c9e2ea3d661a0e5b6bbc ("drm/omap:
>> sdi: Sort includes alphabetically") works...
> 
> The venc issue is fixed in "Switch the HDMI and VENC outputs to drm_bridge", which is a few commits
> after the "venc: Register a drm_bridge".
> 
> So I'm guessing SDI works until "sdi: Register a drm_bridge", but as omapdrm doesn't probe, you get
> no displays.
> 
> Can you try to pinpoint a bit where the hang happens? Maybe add DRM/omapdrm debug prints, or perhaps
> sysrq works and it shows a lock that's in deadlock.

Also, one data point would be to disable venc, e.g. set venc status to "disabled" in dts.

 Tomi

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