linux-kernel - [PATCH 2/2] drm/imx: Remove the primary plane created by create_primary

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Date:	Wed, 4 Nov 2015 18:15:58 +0800
From:	Liu Ying <Ying.Liu@...escale.com>
To:	<dri-devel@...ts.freedesktop.org>
CC:	<linux-kernel@...r.kernel.org>, <p.zabel@...gutronix.de>,
	<airlied@...ux.ie>
Subject: [PATCH 2/2] drm/imx: Remove the primary plane created by create_primary_plane()

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@...4'
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@...escale.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;
+}
+
 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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