linux-kernel - [PATCH v2 1/2] drm/atomic: Allow vblank-enabled + self-refresh "disable"

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Date:   Fri,  6 Jan 2023 17:23:22 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Heiko Stübner <heiko@...ech.de>,
        Daniel Vetter <daniel@...ll.ch>,
        Sean Paul <seanpaul@...omium.org>
Cc:     Michel Dänzer <michel.daenzer@...lbox.org>,
        Sandy Huang <hjc@...k-chips.com>,
        linux-rockchip@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>, stable@...r.kernel.org
Subject: [PATCH v2 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.

Add a different expectation: that CRTCs *should* leave vblank enabled
when going into self-refresh.

This patch is preparation for another patch -- "drm/rockchip: vop: Leave
vblank enabled in self-refresh" -- which resolves conflicts between the
above self-refresh behavior and the API tests in IGT's kms_vblank test
module.

v2:
 * add 'ret != 0' warning case for self-refresh
 * describe failing test case and relation to drm/rockchip patch better

Cc: <stable@...r.kernel.org> # dependency for "drm/rockchip: vop: Leave
                             # vblank enabled in self-refresh"
Signed-off-by: Brian Norris <briannorris@...omium.org>
---
 drivers/gpu/drm/drm_atomic_helper.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index d579fd8f7cb8..a22485e3e924 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1209,7 +1209,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 			continue;

 		ret = drm_crtc_vblank_get(crtc);
-		WARN_ONCE(ret != -EINVAL, "driver forgot to call drm_crtc_vblank_off()\n");
+		/*
+		 * Self-refresh is not a true "disable"; ensure vblank remains
+		 * enabled.
+		 */
+		if (new_crtc_state->self_refresh_active)
+			WARN_ONCE(ret != 0,
+				  "driver disabled vblank in self-refresh\n");
+		else
+			WARN_ONCE(ret != -EINVAL,
+				  "driver forgot to call drm_crtc_vblank_off()\n");
 		if (ret == 0)
 			drm_crtc_vblank_put(crtc);
 	}
-- 
2.39.0.314.g84b9a713c41-goog