linux-kernel - [PATCH 5.15 139/207] drm/vc4: kms: Wait for the commit before increasing our clock rate

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Date:   Mon,  6 Dec 2021 15:56:33 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxime Ripard <maxime@...no.tech>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Jian-Hong Pan <jhp@...lessos.org>
Subject: [PATCH 5.15 139/207] drm/vc4: kms: Wait for the commit before increasing our clock rate

From: Maxime Ripard <maxime@...no.tech>

commit 0c980a006d3fbee86c4d0698f66d6f5381831787 upstream.

Several DRM/KMS atomic commits can run in parallel if they affect
different CRTC. These commits share the global HVS state, so we have
some code to make sure we run commits in sequence. This synchronization
code is one of the first thing that runs in vc4_atomic_commit_tail().

Another constraints we have is that we need to make sure the HVS clock
gets a boost during the commit. That code relies on clk_set_min_rate and
will remove the old minimum and set a new one. We also need another,
temporary, minimum for the duration of the commit.

The algorithm is thus to set a temporary minimum, drop the previous
one, do the commit, and finally set the minimum for the current mode.

However, the part that sets the temporary minimum and drops the older
one runs before the commit synchronization code.

Thus, under the proper conditions, we can end up mixing up the minimums
and ending up with the wrong one for our current step.

To avoid it, let's move the clock setup in the protected section.

Fixes: d7d96c00e585 ("drm/vc4: hvs: Boost the core clock during modeset")
Signed-off-by: Maxime Ripard <maxime@...no.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
Tested-by: Jian-Hong Pan <jhp@...lessos.org>
Link: https://lore.kernel.org/r/20211117094527.146275-2-maxime@cerno.tech
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/vc4/vc4_kms.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -353,9 +353,6 @@ static void vc4_atomic_commit_tail(struc
 		vc4_hvs_mask_underrun(dev, vc4_crtc_state->assigned_channel);
 	}

-	if (vc4->hvs->hvs5)
-		clk_set_min_rate(hvs->core_clk, 500000000);
-
 	old_hvs_state = vc4_hvs_get_old_global_state(state);
 	if (!old_hvs_state)
 		return;
@@ -377,6 +374,9 @@ static void vc4_atomic_commit_tail(struc
 			drm_err(dev, "Timed out waiting for commit\n");
 	}

+	if (vc4->hvs->hvs5)
+		clk_set_min_rate(hvs->core_clk, 500000000);
+
 	drm_atomic_helper_commit_modeset_disables(dev, state);

 	vc4_ctm_commit(vc4, state);