linux-kernel - Re: [PATCH 5/5 v3] drm/bridge: adv7511: Reuse __adv7511_power

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Date:   Mon, 16 Jan 2017 18:03:11 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: Re: [PATCH 5/5 v3] drm/bridge: adv7511: Reuse __adv7511_power_on/off() when probing EDID

Hi John,

Thank you for the patch.

On Tuesday 03 Jan 2017 11:41:42 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 somehow getting lost. Using the logic
> in __adv7511_power_on/off() which syncs and dirtys the cache
> avoids this issue.
> 
> Thus this patch changes the EDID probing logic so that we
> re-use the __adv7511_power_on/off() calls.

regcache_sync() is quite costly as it will write a bunch of registers. 
Wouldn't it be more efficient to only write the registers that are needed for 
EDID access ?

> 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 | 17 +++--------------
>  1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c index dbdb71c..24573e0
> 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -572,24 +572,13 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
>  	unsigned int count;
> 
>  	/* Reading the EDID only works if the device is powered */
> -	if (!adv7511->powered) {
> -		regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
> -				   ADV7511_POWER_POWER_DOWN, 0);
> -		if (adv7511->i2c_main->irq) {
> -			regmap_write(adv7511->regmap, 
ADV7511_REG_INT_ENABLE(0),
> -				     ADV7511_INT0_EDID_READY);
> -			regmap_write(adv7511->regmap, 
ADV7511_REG_INT_ENABLE(1),
> -				     ADV7511_INT1_DDC_ERROR);
> -		}
> -		adv7511->current_edid_segment = -1;
> -	}
> +	if (!adv7511->powered)
> +		__adv7511_power_on(adv7511);
> 
>  	edid = drm_do_get_edid(connector, adv7511_get_edid_block, adv7511);
> 
>  	if (!adv7511->powered)
> -		regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
> -				   ADV7511_POWER_POWER_DOWN,
> -				   ADV7511_POWER_POWER_DOWN);
> +		__adv7511_power_off(adv7511);
> 
>  	kfree(adv7511->edid);
>  	adv7511->edid = edid;

-- 
Regards,

Laurent Pinchart