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Subject[PATCH 5.10 054/563] drm/vc4: hdmi: Set a default HSM rate
Date
From: Maxime Ripard <maxime@cerno.tech>

[ Upstream commit 3e85b81591609bb794bb00cd619b20965b5b38cd ]

When the firmware doesn't setup the HSM rate (such as when booting
without an HDMI cable plugged in), its rate is 0 and thus any register
access results in a CPU stall, even though HSM is enabled.

Let's enforce a minimum rate at boot to avoid this issue.

Fixes: 4f6e3d66ac52 ("drm/vc4: Add runtime PM support to the HDMI encoder driver")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Nicolas Saenz Julienne <nsaenz@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenz@kernel.org>
Tested-by: Michael Stapelberg <michael@stapelberg.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210922125419.4125779-4-maxime@cerno.tech
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/vc4/vc4_hdmi.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index ee293f061f0a8..5d5c4e9a86218 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -79,6 +79,7 @@
# define VC4_HD_M_SW_RST BIT(2)
# define VC4_HD_M_ENABLE BIT(0)

+#define HSM_MIN_CLOCK_FREQ 120000000
#define CEC_CLOCK_FREQ 40000
#define VC4_HSM_MID_CLOCK 149985000

@@ -1806,6 +1807,19 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
vc4_hdmi->disable_wifi_frequencies =
of_property_read_bool(dev->of_node, "wifi-2.4ghz-coexistence");

+ /*
+ * If we boot without any cable connected to the HDMI connector,
+ * the firmware will skip the HSM initialization and leave it
+ * with a rate of 0, resulting in a bus lockup when we're
+ * accessing the registers even if it's enabled.
+ *
+ * Let's put a sensible default at runtime_resume so that we
+ * don't end up in this situation.
+ */
+ ret = clk_set_min_rate(vc4_hdmi->hsm_clock, HSM_MIN_CLOCK_FREQ);
+ if (ret)
+ goto err_put_ddc;
+
if (vc4_hdmi->variant->reset)
vc4_hdmi->variant->reset(vc4_hdmi);

--
2.34.1


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