Re: [PATCH 2/2] drm/imx: Remove the primary plane created by create_primary_plane()

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Nov 04, 2015 at 06:15:58PM +0800, Liu Ying wrote:
> Since we are using ipu_plane_init() to add one primary plane for each
> IPU CRTC, it's unnecessary to create the safe one by using the helper
> create_primary_plane().
> 
> Furthermore, the safe one is attached to crtc->primary, which actually
> carries a framebuffer(crtc->primary->fb) created by the fbdev helper to
> build up the fbcon.  Instead, the one created by ipu_plane_init() is
> dangling, but it is the one actually does ipu_plane_mode_set() for the
> fbcon.  This may causes the mismatch bewteen ipu_plane->enabled(true) and
> ipu_plane->base.fb(NULL).  Thus, it brings a NULL pointer dereference
> issue in ipu_plane_mode_set() when we try to additionally touch the
> IDMAC channel of the ipu_plane.  This issue could be reproduced by
> running the drm modetest with command line 'modetest -P 19:1024x768@XR24'
> on the i.MX6Q SabreSD platform(single LVDS display).  This patch binds
> the plane created by ipu_plane_init() with crtc->primary and removes the
> safe one to address this issue.
> 
> Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
> ---
>  drivers/gpu/drm/imx/imx-drm-core.c | 3 ++-
>  drivers/gpu/drm/imx/ipuv3-crtc.c   | 6 ++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/imx/imx-drm-core.c b/drivers/gpu/drm/imx/imx-drm-core.c
> index 6faa735..08eceeb 100644
> --- a/drivers/gpu/drm/imx/imx-drm-core.c
> +++ b/drivers/gpu/drm/imx/imx-drm-core.c
> @@ -373,7 +373,8 @@ int imx_drm_add_crtc(struct drm_device *drm, struct drm_crtc *crtc,
>  	drm_crtc_helper_add(crtc,
>  			imx_drm_crtc->imx_drm_helper_funcs.crtc_helper_funcs);
>  
> -	drm_crtc_init(drm, crtc,
> +	/* The related primary plane will be created in ipu_plane_init(). */
> +	drm_crtc_init_with_planes(drm, crtc, NULL, NULL,
>  			imx_drm_crtc->imx_drm_helper_funcs.crtc_funcs);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/imx/ipuv3-crtc.c b/drivers/gpu/drm/imx/ipuv3-crtc.c
> index 8d68697..d27143f 100644
> --- a/drivers/gpu/drm/imx/ipuv3-crtc.c
> +++ b/drivers/gpu/drm/imx/ipuv3-crtc.c
> @@ -343,6 +343,11 @@ err_out:
>  	return ret;
>  }
>  
> +static inline void ipu_crtc_set_primary_plane(struct ipu_crtc *ipu_crtc)
> +{
> +	ipu_crtc->base.primary = &ipu_crtc->plane[0]->base;

This is quite a hack. Better would be to reorg the code so that when you
call drm_crtc_init_with_planes the primary plane has been created already.
-Daniel

> +}
> +
>  static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
>  	struct ipu_client_platformdata *pdata, struct drm_device *drm)
>  {
> @@ -380,6 +385,7 @@ static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
>  			ret);
>  		goto err_remove_crtc;
>  	}
> +	ipu_crtc_set_primary_plane(ipu_crtc);
>  
>  	/* If this crtc is using the DP, add an overlay plane */
>  	if (pdata->dp >= 0 && pdata->dma[1] > 0) {
> -- 
> 2.5.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch