linux-kernel - [PATCH 2/4] drm/vc4: hdmi: Enable power domain before setting minimum

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Message-Id: <20230126-rpi-display-fw-clk-cleanup-v1-2-d646ff6fb842@cerno.tech>
Date:   Thu, 26 Jan 2023 18:05:47 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Emma Anholt <emma@...olt.net>, Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Maxime Ripard <maxime@...no.tech>
Subject: [PATCH 2/4] drm/vc4: hdmi: Enable power domain before setting minimum

On the RaspberryPi0-3, the HSM clock was provided by the clk-bcm2835
driver, but on the Pi4 it was provided by the firmware through the
clk-raspberrypi driver.

The clk-bcm2835 driver registers the HSM clock using the
CLK_SET_RATE_GATE flag that prevents any modification to the rate while
the clock is active.

This meant that we needed to call clk_set_min_rate() before our call to
pm_runtime_resume_and_get() since our runtime_resume implementation
needs to enable the HSM clock for the HDMI controller registers to be
functional.

However, the HSM clock is part of the HDMI power domain which might not
be powered prior to the pm_runtime_resume_and_get() call, so we could
end up changing the rate of the HSM clock while its power domain was
disabled.

We recently changed the backing driver for the RaspberryPi0-3 to
clk-raspberrypi though, which doesn't have such restrictions. We can
thus move the clk_set_min_rate() after our call to runtime_resume and
avoid the access while the power domain is disabled.

Signed-off-by: Maxime Ripard <maxime@...no.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 98fa306dbd24..9dd722b9ae3a 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1466,6 +1466,12 @@ static void vc4_hdmi_encoder_pre_crtc_configure(struct drm_encoder *encoder,
 	if (!drm_dev_enter(drm, &idx))
 		goto out;

+	ret = pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev);
+	if (ret < 0) {
+		DRM_ERROR("Failed to retain power domain: %d\n", ret);
+		goto err_dev_exit;
+	}
+
 	/*
 	 * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
 	 * be faster than pixel clock, infinitesimally faster, tested in
@@ -1488,13 +1494,7 @@ static void vc4_hdmi_encoder_pre_crtc_configure(struct drm_encoder *encoder,
 	ret = clk_set_min_rate(vc4_hdmi->hsm_clock, hsm_rate);
 	if (ret) {
 		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
-		goto err_dev_exit;
-	}
-
-	ret = pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev);
-	if (ret < 0) {
-		DRM_ERROR("Failed to retain power domain: %d\n", ret);
-		goto err_dev_exit;
+		goto err_put_runtime_pm;
 	}

 	ret = clk_set_rate(vc4_hdmi->pixel_clock, tmds_char_rate);

-- 
2.39.1