[PATCH v2] drm: Add checks for NULL drm_*_helper_funcs

[Daniel Vetter]

On Wed, May 30, 2018 at 03:42:59AM +0300, Haneen Mohammed wrote:
> This patch add checks for NULL drm_[connector/crtc/plane]_helper_funcs
> pointers before derefrencing the variable to avoid NULL pointer
> dereference and make the helper functions optional in the following
> cases:
> 
> 1) when using drm_helper_probe_single_connector_modes for fill_modes
> callback in the drm_connector_funcs.
> 2) using drm_atomic_helper_[check/commit] for atomic_[check/commit]
> callbacks in the drm_mode_config_funcs.
> 
> The dependency is as follow:
> 
> drm_connector_funcs:
> * fill_modes = drm_helper_probe_single_connector_modes
> 	b) drm_helper_probe_detect -> drm_connector_helper_funcs
> 
> drm_mode_config_funcs:
> * atomic_check = drm_atomic_helper_check
> 	a) drm_atomic_helper_check_modeset -> drm_connector helper_funcs
> 	a) handle_conflicting_encoders -> drm_connector_helper_funcs
> 	b) mode_fixup -> drm_crtc_helper_funcs
> 	c) update_connector_routing -> drm_connectot_helper_funcs
> 
> * atomic_commit = drm_atomic_helper_commit
> 	a) drm_atomic_helper_prepare_planes -> drm_plane_helper_funcs
> 	b) drm_atomic_helper_cleanup_planes -> drm_plane_helper_funcs
> 
> Signed-off-by: Haneen Mohammed <hamohammed.sa at gmail.com>

Ok, I think making drm_connector_helper_funcs optional makes some sense -
->best_connector has a default implemenation that works for almost
everyone, and if you don't have a way to detect the output it's silly to
have a default implementation that does nothing.

But making the plane/crtc funcs optional gives you a driver which does
exactly nothing, and that's not terribly useful.

I think respinning this to just make drm_connector_helper_funcs optional
is reasonable, and for all others we need to start making vkms functional
:-)

Cheers, Daniel

> ---
> Chanes in v2:
> - add the least amount of checks to make the helpers optional for vkms
> 
>  drivers/gpu/drm/drm_atomic_helper.c | 16 ++++++++--------
>  drivers/gpu/drm/drm_probe_helper.c  |  5 +++--
>  2 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 2a7ceca82b9e..ff3684c4a83c 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -112,9 +112,9 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state,
>  		if (!new_conn_state->crtc)
>  			continue;
>  
> -		if (funcs->atomic_best_encoder)
> +		if (funcs && funcs->atomic_best_encoder)
>  			new_encoder = funcs->atomic_best_encoder(connector, new_conn_state);
> -		else if (funcs->best_encoder)
> +		else if (funcs && funcs->best_encoder)
>  			new_encoder = funcs->best_encoder(connector);
>  		else
>  			new_encoder = drm_atomic_helper_best_encoder(connector);
> @@ -308,10 +308,10 @@ update_connector_routing(struct drm_atomic_state *state,
>  
>  	funcs = connector->helper_private;
>  
> -	if (funcs->atomic_best_encoder)
> +	if (funcs && funcs->atomic_best_encoder)
>  		new_encoder = funcs->atomic_best_encoder(connector,
>  							 new_connector_state);
> -	else if (funcs->best_encoder)
> +	else if (funcs && funcs->best_encoder)
>  		new_encoder = funcs->best_encoder(connector);
>  	else
>  		new_encoder = drm_atomic_helper_best_encoder(connector);
> @@ -438,7 +438,7 @@ mode_fixup(struct drm_atomic_state *state)
>  			continue;
>  
>  		funcs = crtc->helper_private;
> -		if (!funcs->mode_fixup)
> +		if (!funcs || !funcs->mode_fixup)
>  			continue;
>  
>  		ret = funcs->mode_fixup(crtc, &new_crtc_state->mode,
> @@ -639,7 +639,7 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>  				new_crtc_state->connectors_changed = true;
>  		}
>  
> -		if (funcs->atomic_check)
> +		if (funcs && funcs->atomic_check)
>  			ret = funcs->atomic_check(connector, new_connector_state);
>  		if (ret)
>  			return ret;
> @@ -2117,7 +2117,7 @@ int drm_atomic_helper_prepare_planes(struct drm_device *dev,
>  
>  		funcs = plane->helper_private;
>  
> -		if (funcs->prepare_fb) {
> +		if (funcs && funcs->prepare_fb) {
>  			ret = funcs->prepare_fb(plane, new_plane_state);
>  			if (ret)
>  				goto fail;
> @@ -2412,7 +2412,7 @@ void drm_atomic_helper_cleanup_planes(struct drm_device *dev,
>  
>  		funcs = plane->helper_private;
>  
> -		if (funcs->cleanup_fb)
> +		if (funcs && funcs->cleanup_fb)
>  			funcs->cleanup_fb(plane, plane_state);
>  	}
>  }
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 527743394150..2fea54d16ebb 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -320,7 +320,7 @@ drm_helper_probe_detect(struct drm_connector *connector,
>  	if (ret)
>  		return ret;
>  
> -	if (funcs->detect_ctx)
> +	if (funcs && funcs->detect_ctx)
>  		return funcs->detect_ctx(connector, ctx, force);
>  	else if (connector->funcs->detect)
>  		return connector->funcs->detect(connector, force);
> @@ -480,7 +480,8 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  		goto prune;
>  	}
>  
> -	count = (*connector_funcs->get_modes)(connector);
> +	if (connector_funcs && connector_funcs->get_modes)
> +		count = (*connector_funcs->get_modes)(connector);
>  
>  	if (count == 0 && connector->status == connector_status_connected)
>  		count = drm_add_modes_noedid(connector, 1024, 768);
> -- 
> 2.17.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch