[PATCH 02/13] drm/meson: dw-hdmi: Protect from possible NULL pointer dereference

[Jonas Karlman]

The IRQ handler can be called at any time after the call to
devm_request_threaded_irq() completes, even before dw_hdmi->bridge has
been assigned later in meson_dw_hdmi_bind().

Protect from a possible NULL pointer dereference in IRQ handler by only
calling drm_helper_hpd_irq_event() when bridge has been assigned.

Fixes: e67f6037ae1b ("drm/meson: split out encoder from meson_dw_hdmi")
Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
---
I only observed this NULL pointer dereference one time, without being
able to reliably re-create a similar timing scenario. I still think this
is an issue that possible could happen and likely should be fixed.

Note that patches later in this series will fully replace this change.
---
 drivers/gpu/drm/meson/meson_dw_hdmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/meson/meson_dw_hdmi.c b/drivers/gpu/drm/meson/meson_dw_hdmi.c
index 993f6d5d4b29..eafe7daf6ff1 100644
--- a/drivers/gpu/drm/meson/meson_dw_hdmi.c
+++ b/drivers/gpu/drm/meson/meson_dw_hdmi.c
@@ -520,7 +520,8 @@ static irqreturn_t dw_hdmi_top_thread_irq(int irq, void *dev_id)
 	u32 stat = dw_hdmi->irq_stat;
 
 	/* HPD Events */
-	if (stat & (HDMITX_TOP_INTR_HPD_RISE | HDMITX_TOP_INTR_HPD_FALL)) {
+	if (stat & (HDMITX_TOP_INTR_HPD_RISE | HDMITX_TOP_INTR_HPD_FALL) &&
+	    dw_hdmi->bridge) {
 		bool hpd_connected = false;
 
 		if (stat & HDMITX_TOP_INTR_HPD_RISE)
-- 
2.54.0