Re: [PATCH] drm/rockchip: fix fbdev crash when not use DRM_FBDEV_EMULATION

[Daniel Vetter]

On Wed, Aug 03, 2016 at 04:13:45PM +0800, Mark Yao wrote:
> [    1.162571] Unable to handle kernel NULL pointer dereference at virtual address 00000200
> [    1.165656] Modules linked in:
> [    1.165941] CPU: 5 PID: 143 Comm: kworker/5:2 Not tainted 4.4.15 #237
> [    1.166506] Hardware name: Rockchip RK3399 Evaluation Board v1 (Android) (DT)
> [    1.167153] Workqueue: events output_poll_execute
> [    1.168231] PC is at mutex_lock+0x14/0x44
> [    1.168586] LR is at drm_fb_helper_hotplug_event+0x28/0xcc
> [    1.172192] [<ffffff8008982110>] mutex_lock+0x14/0x44
> [    1.172196] [<ffffff80084025a4>] drm_fb_helper_hotplug_event+0x28/0xcc
> [    1.172201] [<ffffff8008427ae4>] rockchip_drm_output_poll_changed+0x14/0x1c
> [    1.172204] [<ffffff80083f7c4c>] drm_kms_helper_hotplug_event+0x28/0x34
> [    1.172207] [<ffffff80083f7ddc>] output_poll_execute+0x150/0x198
> [    1.172212] [<ffffff80080b0ea8>] process_one_work+0x218/0x3dc
> [    1.172215] [<ffffff80080b1578>] worker_thread+0x24c/0x374
> [    1.172217] [<ffffff80080b5bcc>] kthread+0xdc/0xe4
> [    1.172222] [<ffffff8008084cd0>] ret_from_fork+0x10/0x40
> 
> Signed-off-by: Mark Yao <mark.yao@xxxxxxxxxxxxxx>

Erhm, how exactly did you manage to blow up in there? Without fbdev
support enable drm_fb_helper_hotplug_event() does nothing at all.

The fbdev helper is designed such that you _don't_ have to check for NULL
everywhere in the driver, that would be pretty bad code.
-Daniel

> ---
>  drivers/gpu/drm/rockchip/rockchip_drm_drv.c   | 13 ++++++++++---
>  drivers/gpu/drm/rockchip/rockchip_drm_drv.h   |  8 ++++++--
>  drivers/gpu/drm/rockchip/rockchip_drm_fb.c    |  6 +++---
>  drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c | 26 +++++++++++++++++---------
>  4 files changed, 36 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> index a822d49..1a4dad6 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> @@ -261,7 +261,10 @@ static void rockchip_drm_lastclose(struct drm_device *dev)
>  {
>  	struct rockchip_drm_private *priv = dev->dev_private;
>  
> -	drm_fb_helper_restore_fbdev_mode_unlocked(&priv->fbdev_helper);
> +	if (!priv->fbdev)
> +		return;
> +
> +	drm_fb_helper_restore_fbdev_mode_unlocked(&priv->fbdev->fbdev_helper);
>  }
>  
>  static const struct file_operations rockchip_drm_driver_fops = {
> @@ -310,8 +313,10 @@ void rockchip_drm_fb_suspend(struct drm_device *drm)
>  {
>  	struct rockchip_drm_private *priv = drm->dev_private;
>  
> +	if (!priv->fbdev)
> +		return;
>  	console_lock();
> -	drm_fb_helper_set_suspend(&priv->fbdev_helper, 1);
> +	drm_fb_helper_set_suspend(&priv->fbdev->fbdev_helper, 1);
>  	console_unlock();
>  }
>  
> @@ -319,8 +324,10 @@ void rockchip_drm_fb_resume(struct drm_device *drm)
>  {
>  	struct rockchip_drm_private *priv = drm->dev_private;
>  
> +	if (!priv->fbdev)
> +		return;
>  	console_lock();
> -	drm_fb_helper_set_suspend(&priv->fbdev_helper, 0);
> +	drm_fb_helper_set_suspend(&priv->fbdev->fbdev_helper, 0);
>  	console_unlock();
>  }
>  
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.h b/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
> index ea39329..c054fc2 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
> @@ -50,6 +50,11 @@ struct rockchip_crtc_state {
>  #define to_rockchip_crtc_state(s) \
>  		container_of(s, struct rockchip_crtc_state, base)
>  
> +struct rockchip_drm_fbdev {
> +	struct drm_fb_helper fbdev_helper;
> +	struct drm_gem_object *fbdev_bo;
> +};
> +
>  /*
>   * Rockchip drm private structure.
>   *
> @@ -57,8 +62,7 @@ struct rockchip_crtc_state {
>   * @num_pipe: number of pipes for this device.
>   */
>  struct rockchip_drm_private {
> -	struct drm_fb_helper fbdev_helper;
> -	struct drm_gem_object *fbdev_bo;
> +	struct rockchip_drm_fbdev *fbdev;
>  	const struct rockchip_crtc_funcs *crtc_funcs[ROCKCHIP_MAX_CRTC];
>  	struct drm_atomic_state *state;
>  };
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> index 55c5273..fef6f8d 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> @@ -156,10 +156,10 @@ err_gem_object_unreference:
>  static void rockchip_drm_output_poll_changed(struct drm_device *dev)
>  {
>  	struct rockchip_drm_private *private = dev->dev_private;
> -	struct drm_fb_helper *fb_helper = &private->fbdev_helper;
> +	struct rockchip_drm_fbdev *fbdev = private->fbdev;
>  
> -	if (fb_helper)
> -		drm_fb_helper_hotplug_event(fb_helper);
> +	if (fbdev)
> +		drm_fb_helper_hotplug_event(&fbdev->fbdev_helper);
>  }
>  
>  static void rockchip_crtc_wait_for_update(struct drm_crtc *crtc)
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c b/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> index 207e01d..cc5781a 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> @@ -22,16 +22,16 @@
>  #include "rockchip_drm_fb.h"
>  
>  #define PREFERRED_BPP		32
> -#define to_drm_private(x) \
> -		container_of(x, struct rockchip_drm_private, fbdev_helper)
> +#define to_rockchip_fbdev(x) \
> +		container_of(x, struct rockchip_drm_fbdev, fbdev_helper)
>  
>  static int rockchip_fbdev_mmap(struct fb_info *info,
>  			       struct vm_area_struct *vma)
>  {
>  	struct drm_fb_helper *helper = info->par;
> -	struct rockchip_drm_private *private = to_drm_private(helper);
> +	struct rockchip_drm_fbdev *fbdev = to_rockchip_fbdev(helper);
>  
> -	return rockchip_gem_mmap_buf(private->fbdev_bo, vma);
> +	return rockchip_gem_mmap_buf(fbdev->fbdev_bo, vma);
>  }
>  
>  static struct fb_ops rockchip_drm_fbdev_ops = {
> @@ -50,7 +50,7 @@ static struct fb_ops rockchip_drm_fbdev_ops = {
>  static int rockchip_drm_fbdev_create(struct drm_fb_helper *helper,
>  				     struct drm_fb_helper_surface_size *sizes)
>  {
> -	struct rockchip_drm_private *private = to_drm_private(helper);
> +	struct rockchip_drm_fbdev *fbdev = to_rockchip_fbdev(helper);
>  	struct drm_mode_fb_cmd2 mode_cmd = { 0 };
>  	struct drm_device *dev = helper->dev;
>  	struct rockchip_gem_object *rk_obj;
> @@ -75,7 +75,7 @@ static int rockchip_drm_fbdev_create(struct drm_fb_helper *helper,
>  	if (IS_ERR(rk_obj))
>  		return -ENOMEM;
>  
> -	private->fbdev_bo = &rk_obj->base;
> +	fbdev->fbdev_bo = &rk_obj->base;
>  
>  	fbi = drm_fb_helper_alloc_fbi(helper);
>  	if (IS_ERR(fbi)) {
> @@ -85,7 +85,7 @@ static int rockchip_drm_fbdev_create(struct drm_fb_helper *helper,
>  	}
>  
>  	helper->fb = rockchip_drm_framebuffer_init(dev, &mode_cmd,
> -						   private->fbdev_bo);
> +						   fbdev->fbdev_bo);
>  	if (IS_ERR(helper->fb)) {
>  		dev_err(dev->dev, "Failed to allocate DRM framebuffer.\n");
>  		ret = PTR_ERR(helper->fb);
> @@ -130,6 +130,7 @@ static const struct drm_fb_helper_funcs rockchip_drm_fb_helper_funcs = {
>  int rockchip_drm_fbdev_init(struct drm_device *dev)
>  {
>  	struct rockchip_drm_private *private = dev->dev_private;
> +	struct rockchip_drm_fbdev *fbdev;
>  	struct drm_fb_helper *helper;
>  	unsigned int num_crtc;
>  	int ret;
> @@ -139,7 +140,12 @@ int rockchip_drm_fbdev_init(struct drm_device *dev)
>  
>  	num_crtc = dev->mode_config.num_crtc;
>  
> -	helper = &private->fbdev_helper;
> +	fbdev = devm_kzalloc(dev->dev, sizeof(*fbdev), GFP_KERNEL);
> +	if (!fbdev)
> +		return -ENOMEM;
> +
> +	private->fbdev = fbdev;
> +	helper = &fbdev->fbdev_helper;
>  
>  	drm_fb_helper_prepare(dev, helper, &rockchip_drm_fb_helper_funcs);
>  
> @@ -175,7 +181,9 @@ void rockchip_drm_fbdev_fini(struct drm_device *dev)
>  	struct rockchip_drm_private *private = dev->dev_private;
>  	struct drm_fb_helper *helper;
>  
> -	helper = &private->fbdev_helper;
> +	if (!private || private->fbdev)
> +		return;
> +	helper = &private->fbdev->fbdev_helper;
>  
>  	drm_fb_helper_unregister_fbi(helper);
>  	drm_fb_helper_release_fbi(helper);
> -- 
> 1.9.1
> 
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch