linux-kernel - [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

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Date:   Mon, 21 Nov 2016 16:37:31 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org
Subject: [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

Secton 4.1 of the adv7511 programming guide advises one waits
200ms after powering on the chip before trying to communicate
with it via i2c. Not doing so can cause reliability issues when
probing the EDID.

See:
http://www.analog.com/media/en/technical-documentation/user-guides/ADV7511_Programming_Guide.pdf

So this patch simply adds a 200ms sleep at the end of the
power_on path. This greatly improves EDID probing reliabilty
on hotplug with the HiKey device.

Cc: David Airlie <airlied@...ux.ie>
Cc: Archit Taneja <architt@...eaurora.org>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: dri-devel@...ts.freedesktop.org
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
index b240e05..2114a4c 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
@@ -361,6 +361,8 @@ static void __adv7511_power_on(struct adv7511 *adv7511)
 	 */
 	regcache_sync(adv7511->regmap);
 
+	msleep(200);
+
 	if (adv7511->type == ADV7533)
 		adv7533_dsi_power_on(adv7511);
 }
-- 
2.7.4