[PATCH AUTOSEL 6.0 20/34] drm/vc4: hdmi: Check the HSM rate at runtime_resume

Sasha Levin
2022-11-01T11:29:56Z

From: Maxime Ripard <maxime@cerno.tech>

[ Upstream commit 4190e8bbcbc77a9c36724681801cedc5229e7fc2 ]

If our HSM clock has not been properly initialized, any register access
will silently lock up the system.

Let's check that this can't happen by adding a check for the rate before
any register access, and error out otherwise.

Link: https://lore.kernel.org/dri-devel/20220922145448.w3xfywkn5ecak2et@pengutronix.de/
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220929-rpi-pi3-unplugged-fixes-v1-2-cd22e962296c@cerno.tech
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/vc4/vc4_hdmi.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 1e5f68704d7d..3d8fc32b4d08 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -2869,12 +2869,28 @@ static int vc4_hdmi_runtime_resume(struct device *dev)
struct vc4_hdmi *vc4_hdmi = dev_get_drvdata(dev);
unsigned long __maybe_unused flags;
u32 __maybe_unused value;
+ unsigned long rate;
int ret;

ret = clk_prepare_enable(vc4_hdmi->hsm_clock);
if (ret)
return ret;

+ /*
+ * Whenever the RaspberryPi boots without an HDMI monitor
+ * plugged in, the firmware won't have initialized the HSM clock
+ * rate and it will be reported as 0.
+ *
+ * If we try to access a register of the controller in such a
+ * case, it will lead to a silent CPU stall. Let's make sure we
+ * prevent such a case.
+ */
+ rate = clk_get_rate(vc4_hdmi->hsm_clock);
+ if (!rate) {
+ ret = -EINVAL;
+ goto err_disable_clk;
+ }
+
if (vc4_hdmi->variant->reset)
vc4_hdmi->variant->reset(vc4_hdmi);

@@ -2896,6 +2912,10 @@ static int vc4_hdmi_runtime_resume(struct device *dev)
#endif

return 0;
+
+err_disable_clk:
+ clk_disable_unprepare(vc4_hdmi->hsm_clock);
+ return ret;
}

static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
--
2.35.1