linux-kernel - [RFC][PATCH] drm/bridge: adv7511: Re-write the i2c address as it may have been lost

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Message-Id: <1484608611-10956-1-git-send-email-john.stultz@linaro.org>
Date:   Mon, 16 Jan 2017 15:16:51 -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] drm/bridge: adv7511: Re-write the i2c address as it may have been lost

Laurent: Would something like the following be preferred? Seems
to work as well for me..

thanks
-john


I've found that by just turning the chip on and off via the
POWER_DOWN register, I end up getting i2c_transfer errors on
HiKey.

Investigating further, it seems some of the register state in
the regmap cache is somehow getting lost, likely as the device
registers were reset during power off.

Thus this patch simply re-writes the i2c address to the
ADV7511_REG_EDID_I2C_ADDR register to ensure its properly set
before we try to read the EDID data.

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 | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
index 405e460..32c59cb 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
@@ -567,6 +567,8 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
 
 	/* Reading the EDID only works if the device is powered */
 	if (!adv7511->powered) {
+		unsigned int edid_i2c_addr = (adv7511->i2c_main->addr << 1) + 4;
+
 		regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
 				   ADV7511_POWER_POWER_DOWN, 0);
 		if (adv7511->i2c_main->irq) {
@@ -576,6 +578,9 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
 				     ADV7511_INT1_DDC_ERROR);
 		}
 		adv7511->current_edid_segment = -1;
+
+		/* Reset the EDID_I2C_ADDR register as it may have been cleared */
+		regmap_write(adv7511->regmap, ADV7511_REG_EDID_I2C_ADDR, edid_i2c_addr);
 	}
 
 	edid = drm_do_get_edid(connector, adv7511_get_edid_block, adv7511);
-- 
2.7.4