openwrt/target/linux/bcm27xx/patches-5.10/950-0654-drm-vc4-hdmi-Use-a-fixed-rate-for-the-HSM-clock-on-B.patch

From 0e0118339ce920d988c550d9013333c5d948ab08 Mon Sep 17 00:00:00 2001
From: Dom Cobley <popcornmix@gmail.com>
Date: Mon, 28 Jun 2021 16:07:16 +0200
Subject: [PATCH] drm/vc4: hdmi: Use a fixed rate for the HSM clock on
 BCM2835

Before the introduction of the BCM2711 support, the HSM clock rate was
fixed, and was the CEC and audio clock source on the SoCs previously
supported.

The HSM clock is also the source of the internal state machine of the
controller and needs to run faster than the pixel clock. All these
requirements were met by running at 101% of the maximum pixel rate,
meeting the fixed clock requirement for audio and CEC, while remaining
faster than any pixel clock we might need.

However, the BCM2711 brought support for 4k and therefore increased
significantly the rate needed for the HSM, and new, independant, clocks
to feed the audio and CEC clocks. Since the HSM clock can also run much
higher, we also need to lower its rate if possible to reduce its power
consumption.

The CEC support code changes its clock divider when the HSM clock rate
is changed, but the audio support never had a similar feature and will
glitch out if audio is played back during a mode set.

Since the HSM rate was meant to be fixed on the SoCs prior to the
BCM2711 anyway, let's introduce back a fixed HSM rate and fix audio.

Fixes: cd4cb49dc5bb ("drm/vc4: hdmi: Adjust HSM clock rate depending on pixel rate")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 54 +++++++++++++++++++++++-----------
 drivers/gpu/drm/vc4/vc4_hdmi.h |  3 ++
 2 files changed, 40 insertions(+), 17 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -911,23 +911,7 @@ static void vc4_hdmi_encoder_pre_crtc_co
 		return;
 	}
 
-	/*
-	 * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
-	 * be faster than pixel clock, infinitesimally faster, tested in
-	 * simulation. Otherwise, exact value is unimportant for HDMI
-	 * operation." This conflicts with bcm2835's vc4 documentation, which
-	 * states HSM's clock has to be at least 108% of the pixel clock.
-	 *
-	 * Real life tests reveal that vc4's firmware statement holds up, and
-	 * users are able to use pixel clocks closer to HSM's, namely for
-	 * 1920x1200@60Hz. So it was decided to have leave a 1% margin between
-	 * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
-	 * 162MHz.
-	 *
-	 * Additionally, the AXI clock needs to be at least 25% of
-	 * pixel clock, but HSM ends up being the limiting factor.
-	 */
-	hsm_rate = max_t(unsigned long, 120000000, (pixel_rate / 100) * 101);
+	hsm_rate = vc4_hdmi->variant->calc_hsm_clock(vc4_hdmi, pixel_rate);
 	vc4_hdmi->hsm_req = clk_request_start(vc4_hdmi->hsm_clock, hsm_rate);
 	if (IS_ERR(vc4_hdmi->hsm_req)) {
 		DRM_ERROR("Failed to set HSM clock rate: %ld\n", PTR_ERR(vc4_hdmi->hsm_req));
@@ -1143,6 +1127,39 @@ static const struct drm_encoder_helper_f
 	.enable = vc4_hdmi_encoder_enable,
 };
 
+static u32 vc4_hdmi_calc_hsm_clock(struct vc4_hdmi *vc4_hdmi, unsigned long pixel_rate)
+{
+	/*
+	 * Whilst this can vary, all the CEC timings are derived from this
+	 * clock, so make it constant to avoid having to reconfigure CEC on
+	 * every mode change.
+	 */
+
+	return 163682864;
+}
+
+static u32 vc5_hdmi_calc_hsm_clock(struct vc4_hdmi *vc4_hdmi, unsigned long pixel_rate)
+{
+	/*
+	 * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
+	 * be faster than pixel clock, infinitesimally faster, tested in
+	 * simulation. Otherwise, exact value is unimportant for HDMI
+	 * operation." This conflicts with bcm2835's vc4 documentation, which
+	 * states HSM's clock has to be at least 108% of the pixel clock.
+	 *
+	 * Real life tests reveal that vc4's firmware statement holds up, and
+	 * users are able to use pixel clocks closer to HSM's, namely for
+	 * 1920x1200@60Hz. So it was decided to have leave a 1% margin between
+	 * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
+	 * 162MHz.
+	 *
+	 * Additionally, the AXI clock needs to be at least 25% of
+	 * pixel clock, but HSM ends up being the limiting factor.
+	 */
+
+	return max_t(unsigned long, 120000000, (pixel_rate / 100) * 101);
+}
+
 static u32 vc4_hdmi_channel_map(struct vc4_hdmi *vc4_hdmi, u32 channel_mask)
 {
 	int i;
@@ -2336,6 +2353,7 @@ static const struct vc4_hdmi_variant bcm
 	.phy_disable		= vc4_hdmi_phy_disable,
 	.phy_rng_enable		= vc4_hdmi_phy_rng_enable,
 	.phy_rng_disable	= vc4_hdmi_phy_rng_disable,
+	.calc_hsm_clock		= vc4_hdmi_calc_hsm_clock,
 	.channel_map		= vc4_hdmi_channel_map,
 	.supports_hdr		= false,
 };
@@ -2364,6 +2382,7 @@ static const struct vc4_hdmi_variant bcm
 	.phy_disable		= vc5_hdmi_phy_disable,
 	.phy_rng_enable		= vc5_hdmi_phy_rng_enable,
 	.phy_rng_disable	= vc5_hdmi_phy_rng_disable,
+	.calc_hsm_clock		= vc5_hdmi_calc_hsm_clock,
 	.channel_map		= vc5_hdmi_channel_map,
 	.supports_hdr		= true,
 };
@@ -2392,6 +2411,7 @@ static const struct vc4_hdmi_variant bcm
 	.phy_disable		= vc5_hdmi_phy_disable,
 	.phy_rng_enable		= vc5_hdmi_phy_rng_enable,
 	.phy_rng_disable	= vc5_hdmi_phy_rng_disable,
+	.calc_hsm_clock		= vc5_hdmi_calc_hsm_clock,
 	.channel_map		= vc5_hdmi_channel_map,
 	.supports_hdr		= true,
 };
--- a/drivers/gpu/drm/vc4/vc4_hdmi.h
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
@@ -97,6 +97,9 @@ struct vc4_hdmi_variant {
 	/* Callback to disable the RNG in the PHY */
 	void (*phy_rng_disable)(struct vc4_hdmi *vc4_hdmi);
 
+	/* Callback to calculate hsm clock */
+	u32 (*calc_hsm_clock)(struct vc4_hdmi *vc4_hdmi, unsigned long pixel_rate);
+
 	/* Callback to get channel map */
 	u32 (*channel_map)(struct vc4_hdmi *vc4_hdmi, u32 channel_mask);