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

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Message-ID: <20130829181412.GX30088@pengutronix.de>
Date:	Thu, 29 Aug 2013 20:14:12 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Fabio Estevam <fabio.estevam@...escale.com>
Cc:	airlied@...hat.com, daniel.vetter@...ll.ch,
	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 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...

> @@ -564,11 +553,6 @@ int imx_drm_add_encoder(struct drm_encoder *encoder,
>  
>  	mutex_lock(&imxdrm->mutex);
>  
> -	if (imxdrm->references) {
> -		ret = -EBUSY;
> -		goto err_busy;
> -	}

...here...

>  	mutex_lock(&imxdrm->mutex);
>  
> -	if (imxdrm->references) {
> -		ret = -EBUSY;
> -		goto err_busy;
> -	}

...and here.

Sascha

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