ACK: [PATCH] drm/dp_helper: don't return EPROTO for defers (v2)

[Chris J Arges]

Clean cherry-pick, fixes a serious bug.
--chris

On 04/30/2015 01:32 AM, Timo Aaltonen wrote:
> From: Dave Airlie <airlied at redhat.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1450322
> 
> If we get a msg.reply of REPLY_DEFER, we also get an err of 0
> so we fail reads with 0 < size and return -EPROTO instead of trying
> again.
> 
> v2: same fix in i2c code.
> 
> Found writing MST support.
> 
> Reviewed-by: Jani Nikula <jani.nikula at intel.com>
> Reviewed-by: Thierry Reding <treding at nvidia.com>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
> (cherry picked from commit aa17edff0afa893b5ab1dd60d842cc6f42e847b4)
> Signed-off-by: Timo Aaltonen <timo.aaltonen at canonical.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index f4babed..2767148 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -386,11 +386,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
>  			return err;
>  		}
>  
> -		if (err < size)
> -			return -EPROTO;
>  
>  		switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
>  		case DP_AUX_NATIVE_REPLY_ACK:
> +			if (err < size)
> +				return -EPROTO;
>  			return err;
>  
>  		case DP_AUX_NATIVE_REPLY_NACK:
> @@ -599,8 +599,6 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  			return err;
>  		}
>  
> -		if (err < msg->size)
> -			return -EPROTO;
>  
>  		switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
>  		case DP_AUX_NATIVE_REPLY_ACK:
> @@ -639,6 +637,8 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  			 * Both native ACK and I2C ACK replies received. We
>  			 * can assume the transfer was successful.
>  			 */
> +			if (err < msg->size)
> +				return -EPROTO;
>  			return 0;
>  
>  		case DP_AUX_I2C_REPLY_NACK:
>