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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Mar 17, 2015 at 05:22:08PM +0200, Jani Nikula wrote:
> 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.
> 
> As I said IRL, it's a bit unfortunate that setting and resetting of
> DP_AUX_I2C_WRITE_STATUS_UPDATE happen at different levels of the
> abstraction. But I can live with that.
> 
> We also have another problem with reporting short writes in i915,
> hopefully fixed by [1]. Before that gets fixed, can't really r-b.
> 
> BR,
> Jani.
> 
> 
> [1] http://mid.gmane.org/1426605534-5780-1-git-send-email-jani.nikula@intel.com

BTW I notice now that radeon seems to have that same problem. I won't
try to fix that, so just a FYI for the radeon folks...

> 
> >
> > 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;
> > +}
> > +
> >  /*
> >   * 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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> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Ville Syrjälä
Intel OTC
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