linux-kernel - Re: [PATCH 6/6] drm/bridge: adv7511: Re-write the i2c address before EDID probing

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Date:   Thu, 19 Jan 2017 01:06:46 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 6/6] drm/bridge: adv7511: Re-write the i2c address before EDID probing

Hi John,

Thank you for the patch.

On Monday 16 Jan 2017 16:52:52 John Stultz wrote:
> 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 getting lost, likely as the device registers
> were reset during power off.

It's not the state in the regmap cache that is lost, but the state in the 
hardware, indeed because the registers contents are lost when the chip is 
powered down.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> 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>
> ---
> v4: New approach to make the EDID_I2C_ADDR register
>     sane, as suggested by Laurent
> ---
>  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c index d216f61..0ed89ea
> 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -573,9 +573,17 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
>  	unsigned int count;
> 
>  	/* Reading the EDID only works if the device is powered */
> -	if (!adv7511->powered)
> +	if (!adv7511->powered) {
> +		unsigned int edid_i2c_addr =
> +					(adv7511->i2c_main->addr << 1) + 4;
> +
>  		__adv7511_power_on(adv7511);
> 
> +		/* Reset the EDID_I2C_ADDR register as it might be cleared */
> +		regmap_write(adv7511->regmap, ADV7511_REG_EDID_I2C_ADDR,
> +			     edid_i2c_addr);
> +	}
> +
>  	edid = drm_do_get_edid(connector, adv7511_get_edid_block, adv7511);
> 
>  	if (!adv7511->powered)

-- 
Regards,

Laurent Pinchart