[PATCH v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

[CK Hu]

Hi, Bo-Chen:

On Wed, 2022-06-15 at 13:50 +0800, CK Hu wrote:
> Hi, Bo-Chen:
> 
> On Fri, 2022-06-10 at 18:55 +0800, Bo-Chen Chen wrote:
> > From: Markus Schneider-Pargmann <msp at baylibre.com>
> > 
> > This patch adds a embedded displayport driver for the MediaTek
> > mt8195
> > SoC.
> > 
> > It supports the MT8195, the embedded DisplayPort units. It offers
> > DisplayPort 1.4 with up to 4 lanes.
> > 
> > The driver creates a child device for the phy. The child device
> > will
> > never exist without the parent being active. As they are sharing a
> > register range, the parent passes a regmap pointer to the child so
> > that
> > both can work with the same register range. The phy driver sets
> > device
> > data that is read by the parent to get the phy device that can be
> > used
> > to control the phy properties.
> > 
> > This driver is based on an initial version by
> > Jitao shi <jitao.shi at mediatek.com>
> > 
> > Signed-off-by: Markus Schneider-Pargmann <msp at baylibre.com>
> > Signed-off-by: Guillaume Ranquet <granquet at baylibre.com>
> > [Bo-Chen: Cleanup the drivers and modify comments from reviewers]
> > Signed-off-by: Bo-Chen Chen <rex-bc.chen at mediatek.com>
> > ---
> 
> [snip]
> 
> > +
> > +static int mtk_dp_train_flow(struct mtk_dp *mtk_dp, u8
> > target_link_rate,
> > +			     u8 target_lane_count)
> > +{
> > +	u8 lane_adjust[2] = {};
> > +	bool pass_tps1 = false;
> > +	bool pass_tps2_3 = false;
> > +	int train_retries;
> > +	int status_control;
> > +	int iteration_count;
> > +	int ret;
> > +	u8 prev_lane_adjust;
> > +
> > +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LINK_BW_SET,
> > target_link_rate);
> > +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LANE_COUNT_SET,
> > +			   target_lane_count |
> > DP_LANE_COUNT_ENHANCED_FRAME_EN);
> > +
> > +	if (mtk_dp->train_info.sink_ssc)
> > +		drm_dp_dpcd_writeb(&mtk_dp->aux, DP_DOWNSPREAD_CTRL,
> > +				   DP_SPREAD_AMP_0_5);
> > +
> > +	train_retries = 0;
> > +	status_control = 0;
> > +	iteration_count = 1;
> > +	prev_lane_adjust = 0xFF;
> > +
> > +	mtk_dp_set_lanes(mtk_dp, target_lane_count / 2);
> > +	ret = mtk_dp_phy_configure(mtk_dp, target_link_rate,
> > target_lane_count);
> > +	if (ret)
> > +		return -EINVAL;
> > +
> > +	dev_dbg(mtk_dp->dev,
> > +		"Link train target_link_rate = 0x%x, target_lane_count
> > = 0x%x\n",
> > +		target_link_rate, target_lane_count);
> > +
> > +	do {
> > +		train_retries++;
> > +		if (!mtk_dp->train_info.cable_plugged_in ||
> > +		    mtk_dp->train_info.irq_sta.hpd_disconnect) {
> > +			return -ENODEV;
> > +		}
> > +
> > +		if (mtk_dp->train_state < MTK_DP_TRAIN_STATE_TRAINING)
> 
> This checking would never be true, so remove it.
> 
> > +			return -EAGAIN;
> > +
> > +		if (!pass_tps1) {
> > +			ret = mtk_dp_train_tps_1(mtk_dp,
> > target_lane_count,
> > +						 &iteration_count,
> > lane_adjust,
> > +						 &status_control,
> > +						 &prev_lane_adjust);
> > +			if (!ret) {
> > +				pass_tps1 = true;
> > +				train_retries = 0;
> > +			} else if (ret == -EINVAL) {
> > +				break;
> > +			}
> > +		} else {
> > +			ret = mtk_dp_train_tps_2_3(mtk_dp,
> > target_link_rate,
> > +						   target_lane_count,
> > +						   &iteration_count,
> > +						   lane_adjust,
> > &status_control,
> > +						   &prev_lane_adjust);
> > +			if (!ret) {
> > +				pass_tps2_3 = true;
> > +				break;
> > +			} else if (ret == -EINVAL) {
> > +				break;
> > +			}
> > +		}
> > +
> > +		drm_dp_dpcd_read(&mtk_dp->aux,
> > DP_ADJUST_REQUEST_LANE0_1,
> > +				 lane_adjust, sizeof(lane_adjust));
> > +		mtk_dp_train_update_swing_pre(mtk_dp,
> > target_lane_count,
> > +					      lane_adjust);
> > +	} while (train_retries < MTK_DP_TRAIN_RETRY_LIMIT &&
> > +		 iteration_count < MTK_DP_TRAIN_MAX_ITERATIONS);
> 
> mtk_dp_train_tps_1() & mtk_dp_train_tps_2_3() would only be called
> once
> and never be called twice, so remove this loop.

Sorry, mtk_dp_train_tps_1() & mtk_dp_train_tps_2_3() may return
-EAGAIN, so keep this loop.

> 
> Regards,
> CK
> 
> > +
> > +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_TRAINING_PATTERN_SET,
> > +			   DP_TRAINING_PATTERN_DISABLE);
> > +	ret = mtk_dp_train_set_pattern(mtk_dp, 0);
> > +	if (ret)
> > +		return -EINVAL;
> > +
> > +	if (!pass_tps2_3)
> > +		return -ETIMEDOUT;
> > +
> > +	mtk_dp->train_info.link_rate = target_link_rate;
> > +	mtk_dp->train_info.lane_count = target_lane_count;
> > +
> > +	mtk_dp_training_set_scramble(mtk_dp, true);
> > +
> > +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LANE_COUNT_SET,
> > +			   target_lane_count |
> > +				   DP_LANE_COUNT_ENHANCED_FRAME_EN);
> > +	mtk_dp_set_enhanced_frame_mode(mtk_dp, true);
> > +
> > +	return ret;
> > +}