From 3e85b81591609bb794bb00cd619b20965b5b38cd Mon Sep 17 00:00:00 2001
From: Maxime Ripard <maxime@cerno.tech>
Date: Wed, 22 Sep 2021 14:54:17 +0200
Subject: [PATCH] drm/vc4: hdmi: Set a default HSM rate
Git-commit: 3e85b81591609bb794bb00cd619b20965b5b38cd
Patch-mainline: v5.17-rc1
References: git-fixes

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
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/vc4/vc4_hdmi.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- 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
 
@@ -1809,6 +1810,19 @@ static int vc4_hdmi_bind(struct device *
 	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);