linux-kernel - [PATCH v2] arm64: dts: mediatek: mt8192-asurada: Add off-on-delay-us for pp3300

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Date: Thu,  2 May 2024 23:39:51 +0800
From: Pin-yen Lin <treapking@...omium.org>
To: Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Nícolas F . R . A . Prado <nfraprado@...labora.com>,
	linux-mediatek@...ts.infradead.org,
	Hsin-Te Yuan <yuanhsinte@...omium.org>,
	devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Pin-yen Lin <treapking@...omium.org>
Subject: [PATCH v2] arm64: dts: mediatek: mt8192-asurada: Add off-on-delay-us for pp3300_mipibrdg

Set off-on-delay-us to 500000 us for pp3300_mipibrdg to make sure it
complies with the panel's unprepare delay (the time to power down
completely) of the power sequence. Explicit configuration on the
regulator node is required because mt8192-asurada uses the same power
supply for the panel and the anx7625 DP bridge.

For example, the power sequence could be violated in this sequence:
1. Bridge on: panel goes off, but regulator doesn't turn off (refcount=1).
2. Bridge off: regulator turns off (refcount=0).
3. Bridge resume -> regulator turns on but the bridge driver doesn't
   check the delay.

Or in this sequence:
1. Bridge on: panel goes off. The regulator doesn't turn off (refcount=1),
   but the .unprepared_time in panel_edp is still updated.
2. Bridge off, regulator goes off (refcount=0).
3. Panel on, but the panel driver uses the wrong .unprepared_time to check
   the unprepare delay.

Fixes: f9f00b1f6b9b ("arm64: dts: mediatek: asurada: Add display regulators")
Signed-off-by: Pin-yen Lin <treapking@...omium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

---

Changes in v2:
- Update the commit message
- Collect review tag

 arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
index 7a704246678f..08d71ddf3668 100644
--- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
@@ -147,6 +147,7 @@ pp3300_mipibrdg: regulator-3v3-mipibrdg {
 		regulator-boot-on;
 		gpio = <&pio 127 GPIO_ACTIVE_HIGH>;
 		vin-supply = <&pp3300_g>;
+		off-on-delay-us = <500000>;
 	};

 	/* separately switched 3.3V power rail */
-- 
2.45.0.rc0.197.gbae5840b3b-goog