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

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Date:	Thu, 29 Aug 2013 20:31:14 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Fabio Estevam <fabio.estevam@...escale.com>, airlied@...hat.com,
	gregkh@...uxfoundation.org, festevam@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] imx-drm: Fix probe failure

On Thu, Aug 29, 2013 at 05:21:30PM +0200, Daniel Vetter 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>
> 
> Yeah, just ripping out the imxdrm->references stuff will restore imx, but
> of course all the funny races are still fundamentally there. So we still
> rely on userspace being really careful to obey the right module loading
> sequence and not start any drm client before that has all completed. So
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> Greg, when you slurp this in can you pls also add the imx todo entry from
> the other thread?
> 
> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg43698.html


You said there:

> +- Fix up the driver load sequence to make sure all submodules for encoders/crtcs
> +  are fully loaded before the drm driver is registered.

We can't know when all submodules are registered and really I think this
is not necessary. The driver will use the components available during
open time. When being opened no components will be registered/deregistered.
So a user will always get a functional drm device with the components he
actually loaded.

Sascha

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