Re: [PATCH 5/5] drm/dp: Use I2C_WRITE_STATUS_UPDATE to drain partial I2C_WRITE requests

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 13 Mar 2015, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> When an i2c WRITE gets an i2c defer or short i2c ack reply, we are
> supposed to switch the request from I2C_WRITE to I2C_WRITE_STATUS_UPDATE
> when we continue to poll for the completion of the request.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 41 +++++++++++++++++++++++++++++++++++++----
>  1 file changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index d5368ea..4db81a6 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -422,6 +422,25 @@ static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
>  	       I2C_FUNC_10BIT_ADDR;
>  }
>  
> +static void drm_dp_i2c_msg_set_request(struct drm_dp_aux_msg *msg,
> +				       const struct i2c_msg *i2c_msg)
> +{
> +	msg->request = (i2c_msg->flags & I2C_M_RD) ?
> +		DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
> +	msg->request |= DP_AUX_I2C_MOT;
> +}
> +
> +static void drm_dp_i2c_msg_write_status_update(struct drm_dp_aux_msg *msg)
> +{
> +	/*
> +	 * In case of i2c defer or short i2c ack reply to a write,
> +	 * we need to switch to WRITE_STATUS_UPDATE to drain the
> +	 * rest of the message
> +	 */
> +	if ((msg->request & ~DP_AUX_I2C_MOT) == DP_AUX_I2C_WRITE)
> +		msg->request |= DP_AUX_I2C_WRITE_STATUS_UPDATE;

This only works because DP_AUX_I2C_WRITE == 0, and it may not be obvious
to the casual reader that DP_AUX_I2C_WRITE_STATUS_UPDATE is a
replacement not an addition to DP_AUX_I2C_WRITE.

Whether you fix that or not, this is

Reviewed-by: Jani Nikula <jani.nikula@intel.com>



> +}
> +
>  /*
>   * Transfer a single I2C-over-AUX message and handle various error conditions,
>   * retrying the transaction as appropriate.  It is assumed that the
> @@ -490,6 +509,8 @@ 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 (ret != msg->size)
> +				drm_dp_i2c_msg_write_status_update(msg);
>  			return ret;
>  
>  		case DP_AUX_I2C_REPLY_NACK:
> @@ -501,6 +522,7 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  			DRM_DEBUG_KMS("I2C defer\n");
>  			aux->i2c_defer_count++;
>  			usleep_range(400, 500);
> +			drm_dp_i2c_msg_write_status_update(msg);
>  			continue;
>  
>  		default:
> @@ -566,10 +588,7 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  
>  	for (i = 0; i < num; i++) {
>  		msg.address = msgs[i].addr;
> -		msg.request = (msgs[i].flags & I2C_M_RD) ?
> -			DP_AUX_I2C_READ :
> -			DP_AUX_I2C_WRITE;
> -		msg.request |= DP_AUX_I2C_MOT;
> +		drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
>  		/* Send a bare address packet to start the transaction.
>  		 * Zero sized messages specify an address only (bare
>  		 * address) transaction.
> @@ -577,6 +596,13 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  		msg.buffer = NULL;
>  		msg.size = 0;
>  		err = drm_dp_i2c_do_msg(aux, &msg);
> +
> +		/*
> +		 * Reset msg.request in case in case it got
> +		 * changed into a WRITE_STATUS_UPDATE.
> +		 */
> +		drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
> +
>  		if (err < 0)
>  			break;
>  		/* We want each transaction to be as large as possible, but
> @@ -589,6 +615,13 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  			msg.size = min(transfer_size, msgs[i].len - j);
>  
>  			err = drm_dp_i2c_drain_msg(aux, &msg);
> +
> +			/*
> +			 * Reset msg.request in case in case it got
> +			 * changed into a WRITE_STATUS_UPDATE.
> +			 */
> +			drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
> +
>  			if (err < 0)
>  				break;
>  			transfer_size = err;
> -- 
> 2.0.5
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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