[RFC] 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@linux.ie>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>

---
 drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 5 +++++
 1 file changed, 5 insertions(+)

-- 
2.7.4

Hi John,

Thank you for the patch.

On Monday 16 Jan 2017 15:16:51 John Stultz wrote:
> Laurent: Would something like the following be preferred? Seems

> to work as well for me..


That looks good to me. Feel free to still de-duplicate the power on/off code 
if you want (but of course without adding the regcache_sync to the common 
power on function this time).

Please see below for an additional comment.

> 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@linux.ie>

> Cc: Archit Taneja <architt@codeaurora.org>

> Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>

> Cc: Lars-Peter Clausen <lars@metafoo.de>

> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> Cc: dri-devel@lists.freedesktop.org

> Signed-off-by: John Stultz <john.stultz@linaro.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);

As powering the device off called regcache_mark_dirty(), this will perform an 
I2C write and cache the value. If we then try to read the EDID a second time 
without going through a full power on/off sequence, I believe that regmap will 
skip the write the second time, as the cache will contain the same value and 
won't be marked as dirty. Should we call regcache_mark_dirty() when powering 
the device down further down this function ?

>  	}

> 

>  	edid = drm_do_get_edid(connector, adv7511_get_edid_block, adv7511);


-- 
Regards,

Laurent Pinchart