Date: Tue, 17 Nov 2015 10:10:42 +0800
From: Liu Ying <Ying.Liu@freescale.com>
To: Daniel Vetter <daniel@ffwll.ch>
CC: <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>,
        <p.zabel@pengutronix.de>
Subject: Re: [PATCH 2/2] drm/imx: Remove the primary plane created by
 create_primary_plane()
Message-ID: <20151117021040.GA20180@shlinux2>
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On Mon, Nov 16, 2015 at 05:00:21PM +0100, Daniel Vetter wrote:
> 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

Thanks for your comments.
Philipp has generated a patch[1] to address this.
I acked it conditionally.

[1] http://www.spinics.net/lists/dri-devel/msg93700.html

Regards,
Liu Ying

> 
> > +}
> > +
> >  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
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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