linux-kernel - [PATCH] Revert "drm: bridge: analogix/dp: add panel prepare/unprepare in suspend/resume time"

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Message-Id: <20220822180729.1.I8ac5abe3a4c1c6fd5c061686c6e883c22f69022c@changeid>
Date:   Mon, 22 Aug 2022 18:08:04 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>
Cc:     xuqiang36@...wei.com, Doug Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Zhang Zekun <zhangzekun11@...wei.com>,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH] Revert "drm: bridge: analogix/dp: add panel prepare/unprepare in suspend/resume time"

This reverts commit 211f276ed3d96e964d2d1106a198c7f4a4b3f4c0.

For quite some time, core DRM helpers already ensure that any relevant
connectors/CRTCs/etc. are disabled, as well as their associated
components (e.g., bridges) when suspending the system. Thus,
analogix_dp_bridge_{enable,disable}() already get called, which in turn
call drm_panel_{prepare,unprepare}(). This makes these drm_panel_*()
calls redundant.

Besides redundancy, there are a few problems with this handling:

(1) drm_panel_{prepare,unprepare}() are *not* reference-counted APIs and
are not in general designed to be handled by multiple callers --
although some panel drivers have a coarse 'prepared' flag that mitigates
some damage, at least. So at a minimum this is redundant and confusing,
but in some cases, this could be actively harmful.

(2) The error-handling is a bit non-standard. We ignored errors in
suspend(), but handled errors in resume(). And recently, people noticed
that the clk handling is unbalanced in error paths, and getting *that*
right is not actually trivial, given the current way errors are mostly
ignored.

(3) In the particular way analogix_dp_{suspend,resume}() get used (e.g.,
in rockchip_dp_*(), as a late/early callback), we don't necessarily have
a proper PM relationship between the DP/bridge device and the panel
device. So while the DP bridge gets resumed, the panel's parent device
(e.g., platform_device) may still be suspended, and so any prepare()
calls may fail.

So remove the superfluous, possibly-harmful suspend()/resume() handling
of panel state.

Fixes: 211f276ed3d9 ("drm: bridge: analogix/dp: add panel prepare/unprepare in suspend/resume time")
Link: https://lore.kernel.org/all/Yv2CPBD3Picg%2FgVe@google.com/
Signed-off-by: Brian Norris <briannorris@...omium.org>
---

 drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index 8aadcc0aa90b..df9370e0ff23 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1864,12 +1864,6 @@ EXPORT_SYMBOL_GPL(analogix_dp_remove);
 int analogix_dp_suspend(struct analogix_dp_device *dp)
 {
 	clk_disable_unprepare(dp->clock);
-
-	if (dp->plat_data->panel) {
-		if (drm_panel_unprepare(dp->plat_data->panel))
-			DRM_ERROR("failed to turnoff the panel\n");
-	}
-
 	return 0;
 }
 EXPORT_SYMBOL_GPL(analogix_dp_suspend);
@@ -1884,13 +1878,6 @@ int analogix_dp_resume(struct analogix_dp_device *dp)
 		return ret;
 	}

-	if (dp->plat_data->panel) {
-		if (drm_panel_prepare(dp->plat_data->panel)) {
-			DRM_ERROR("failed to setup the panel\n");
-			return -EBUSY;
-		}
-	}
-
 	return 0;
 }
 EXPORT_SYMBOL_GPL(analogix_dp_resume);
-- 
2.37.2.609.g9ff673ca1a-goog