linux-kernel - [PATCH 1/2] drm/atomic: Allow vblank-enabled + self-refresh "disable"

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Message-Id: <20230105174001.1.I3904f697863649eb1be540ecca147a66e42bfad7@changeid>
Date:   Thu,  5 Jan 2023 17:40:17 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Heiko Stübner <heiko@...ech.de>,
        Sean Paul <seanpaul@...omium.org>
Cc:     Sandy Huang <hjc@...k-chips.com>,
        Michel Dänzer <michel.daenzer@...lbox.org>,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org,
        Brian Norris <briannorris@...omium.org>, stable@...r.kernel.org
Subject: [PATCH 1/2] drm/atomic: Allow vblank-enabled + self-refresh "disable"

The self-refresh helper framework overloads "disable" to sometimes mean
"go into self-refresh mode," and this mode activates automatically
(e.g., after some period of unchanging display output). In such cases,
the display pipe is still considered "on", and user-space is not aware
that we went into self-refresh mode. Thus, users may expect that
vblank-related features (such as DRM_IOCTL_WAIT_VBLANK) still work
properly.

However, we trigger the WARN_ONCE() here if a CRTC driver tries to leave
vblank enabled here.

Add a new exception, such that we allow CRTCs to be "disabled" (with
self-refresh active) with vblank interrupts still enabled.

Cc: <stable@...r.kernel.org> # dependency for subsequent patch
Signed-off-by: Brian Norris <briannorris@...omium.org>
---

 drivers/gpu/drm/drm_atomic_helper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index d579fd8f7cb8..7b5eddadebd5 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1207,6 +1207,12 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)

 		if (!drm_dev_has_vblank(dev))
 			continue;
+		/*
+		 * Self-refresh is not a true "disable"; let vblank remain
+		 * enabled.
+		 */
+		if (new_crtc_state->self_refresh_active)
+			continue;

 		ret = drm_crtc_vblank_get(crtc);
 		WARN_ONCE(ret != -EINVAL, "driver forgot to call drm_crtc_vblank_off()\n");
-- 
2.39.0.314.g84b9a713c41-goog