linux-kernel - [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to power-on sequence

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Date:   Mon, 15 Aug 2022 17:39:07 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        rock.chiu@...adetech.corp-partner.google.com
Subject: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to power-on sequence

The double reset power-on sequence is a workaround for the hardware
flaw in some chip that SPI Clock output glitch and cause internal MPU
unable to read firmware correctly. The sequence is suggested in ps8640
application note.

Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
---
 drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index 49107a6cdac18..d7483c13c569b 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -375,6 +375,11 @@ static int __maybe_unused ps8640_resume(struct device *dev)
 	gpiod_set_value(ps_bridge->gpio_reset, 1);
 	usleep_range(2000, 2500);
 	gpiod_set_value(ps_bridge->gpio_reset, 0);
+	/* Double reset for T4 and T5 */
+	msleep(50);
+	gpiod_set_value(ps_bridge->gpio_reset, 1);
+	msleep(50);
+	gpiod_set_value(ps_bridge->gpio_reset, 0);
 
 	/*
 	 * Mystery 200 ms delay for the "MCU to be ready". It's unclear if
-- 
2.37.1.595.g718a3a8f04-goog