drm/vc4: hdmi: Set a default HSM rate

[ 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>

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index ee293f061f0a8706a2997bece79927c6809733fd..5d5c4e9a86218221b85894e70a8a103169e009f5 100644 (file)
--- 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);