[bug report] drm: bridge: cdns-mhdp8546: Fix possible null pointer dereference

[Dan Carpenter]

Hello Aleksandr Mishin,

Commit 935a92a1c400 ("drm: bridge: cdns-mhdp8546: Fix possible null
pointer dereference") from Apr 8, 2024 (linux-next), leads to the
following Smatch static checker warning:

	drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c:2074 cdns_mhdp_atomic_enable()
	warn: inconsistent returns '&mhdp->link_mutex'.

drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
    1986 static void cdns_mhdp_atomic_enable(struct drm_bridge *bridge,
    1987                                     struct drm_bridge_state *bridge_state)
    1988 {
    1989         struct cdns_mhdp_device *mhdp = bridge_to_mhdp(bridge);
    1990         struct drm_atomic_state *state = bridge_state->base.state;
    1991         struct cdns_mhdp_bridge_state *mhdp_state;
    1992         struct drm_crtc_state *crtc_state;
    1993         struct drm_connector *connector;
    1994         struct drm_connector_state *conn_state;
    1995         struct drm_bridge_state *new_state;
    1996         const struct drm_display_mode *mode;
    1997         u32 resp;
    1998         int ret;
    1999 
    2000         dev_dbg(mhdp->dev, "bridge enable\n");
    2001 
    2002         mutex_lock(&mhdp->link_mutex);
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Holding a lock

    2003 
    2004         if (mhdp->plugged && !mhdp->link_up) {
    2005                 ret = cdns_mhdp_link_up(mhdp);
    2006                 if (ret < 0)
    2007                         goto out;
    2008         }
    2009 
    2010         if (mhdp->info && mhdp->info->ops && mhdp->info->ops->enable)
    2011                 mhdp->info->ops->enable(mhdp);
    2012 
    2013         /* Enable VIF clock for stream 0 */
    2014         ret = cdns_mhdp_reg_read(mhdp, CDNS_DPTX_CAR, &resp);
    2015         if (ret < 0) {
    2016                 dev_err(mhdp->dev, "Failed to read CDNS_DPTX_CAR %d\n", ret);
    2017                 goto out;
    2018         }
    2019 
    2020         cdns_mhdp_reg_write(mhdp, CDNS_DPTX_CAR,
    2021                             resp | CDNS_VIF_CLK_EN | CDNS_VIF_CLK_RSTN);
    2022 
    2023         connector = drm_atomic_get_new_connector_for_encoder(state,
    2024                                                              bridge->encoder);
    2025         if (WARN_ON(!connector))
    2026                 goto out;
    2027 
    2028         conn_state = drm_atomic_get_new_connector_state(state, connector);
    2029         if (WARN_ON(!conn_state))
    2030                 goto out;
    2031 
    2032         if (mhdp->hdcp_supported &&
    2033             mhdp->hw_state == MHDP_HW_READY &&
    2034             conn_state->content_protection ==
    2035             DRM_MODE_CONTENT_PROTECTION_DESIRED) {
    2036                 mutex_unlock(&mhdp->link_mutex);
    2037                 cdns_mhdp_hdcp_enable(mhdp, conn_state->hdcp_content_type);
    2038                 mutex_lock(&mhdp->link_mutex);
    2039         }
    2040 
    2041         crtc_state = drm_atomic_get_new_crtc_state(state, conn_state->crtc);
    2042         if (WARN_ON(!crtc_state))
    2043                 goto out;
    2044 
    2045         mode = &crtc_state->adjusted_mode;
    2046 
    2047         new_state = drm_atomic_get_new_bridge_state(state, bridge);
    2048         if (WARN_ON(!new_state))
    2049                 goto out;
    2050 
    2051         if (!cdns_mhdp_bandwidth_ok(mhdp, mode, mhdp->link.num_lanes,
    2052                                     mhdp->link.rate)) {
    2053                 ret = -EINVAL;
    2054                 goto out;
    2055         }
    2056 
    2057         cdns_mhdp_sst_enable(mhdp, mode);
    2058 
    2059         mhdp_state = to_cdns_mhdp_bridge_state(new_state);
    2060 
    2061         mhdp_state->current_mode = drm_mode_duplicate(bridge->dev, mode);
    2062         if (!mhdp_state->current_mode)
    2063                 return;
                         ^^^^^^^
Needs to unlock before returning.

    2064 
    2065         drm_mode_set_name(mhdp_state->current_mode);
    2066 
    2067         dev_dbg(mhdp->dev, "%s: Enabling mode %s\n", __func__, mode->name);
    2068 
    2069         mhdp->bridge_enabled = true;
    2070 
    2071 out:
    2072         mutex_unlock(&mhdp->link_mutex);
    2073         if (ret < 0)
--> 2074                 schedule_work(&mhdp->modeset_retry_work);
    2075 }

regards,
dan carpenter