linux-kernel - Re: [PATCH v2] imx-drm: Fix probe failure

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Message-ID: <CAOMZO5BXowdp87WavAS5t0q2K6nxFvcrAp-WK5anfDub+H+5kA@mail.gmail.com>
Date:	Thu, 29 Aug 2013 15:30:12 -0300
From:	Fabio Estevam <festevam@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Fabio Estevam <fabio.estevam@...escale.com>,
	Dave Airlie <airlied@...hat.com>, daniel.vetter@...ll.ch,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] imx-drm: Fix probe failure

On Thu, Aug 29, 2013 at 3:14 PM, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> On Thu, Aug 29, 2013 at 10:59:22AM -0300, Fabio Estevam wrote:
>> Since commit b5dc0d10 (drm/imx: kill firstopen callback) the following probe
>> failure is seen:
>>
>> [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
>> [drm] No driver support for vblank timestamp query.
>> [drm] Initialized imx-drm 1.0.0 20120507 on minor 0
>> imx-ldb ldb.10: adding encoder failed with -16
>> imx-ldb: probe of ldb.10 failed with error -16
>> imx-ipuv3 2400000.ipu: IPUv3H probed
>> imx-ipuv3 2800000.ipu: IPUv3H probed
>> imx-ipuv3-crtc imx-ipuv3-crtc.0: adding crtc failed with -16.
>> imx-ipuv3-crtc: probe of imx-ipuv3-crtc.0 failed with error -16
>> imx-ipuv3-crtc imx-ipuv3-crtc.1: adding crtc failed with -16.
>> imx-ipuv3-crtc: probe of imx-ipuv3-crtc.1 failed with error -16
>> imx-ipuv3-crtc imx-ipuv3-crtc.2: adding crtc failed with -16.
>> imx-ipuv3-crtc: probe of imx-ipuv3-crtc.2 failed with error -16
>> imx-ipuv3-crtc imx-ipuv3-crtc.3: adding crtc failed with -16.
>> imx-ipuv3-crtc: probe of imx-ipuv3-crtc.3 failed with error -16
>>
>> The reason for the probe failure is that now 'imxdrm->references' is incremented
>> early in imx_drm_driver_load(), so the following checks in imx_drm_add_crtc()
>> and imx_drm_add_encoder():
>>
>>       if (imxdrm->references) {
>>               ret = -EBUSY;
>>               goto err_busy;
>>       }
>>
>> ,will always fail.
>>
>> Let the drm core handle the references instead of doing this manually in
>> imx-drm. In imx-drm-core the open and close callbacks map to drm_open and
>> drm_close, which handle the references via open_count.
>>
>> After this patch, lvds panel is functional on a mx6qsabrelite board.
>>
>> Signed-off-by: Fabio Estevam <fabio.estevam@...escale.com>
>> ---
>> Changes since v1:
>> - Improved commit log by providing an explanation to the probe failure
>> - Cc'ed Dave/Daniel
>>
>> @@ -485,11 +480,6 @@ int imx_drm_add_crtc(struct drm_crtc *crtc,
>>
>>       mutex_lock(&imxdrm->mutex);
>>
>> -     if (imxdrm->references) {
>> -             ret = -EBUSY;
>> -             goto err_busy;
>> -     }
>
> As I told in v1: Simply removing the code is not an option. We agreed
> that we use the drm core reference counting, so you must actually test
> for it here...

Yes, we did, but after reading a separate thread on this topic, I
learned that drm core does not support it currently.

Daniel mentions [1]: "And I wouldn't worry about module unloading and
refcounting for
now since core drm is terminally broken in that area already anyway"

[1] http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg43698.html

Can't we just apply this patch so that imx-drm can be functional again
and fix module unloading/refcount later?
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