Re: [PATCH v16 3/8] drm/mediatek: Add MT8195 Embedded DisplayPort driver

[CK Hu <ck.hu@mediatek.com>]

Hi, Bo-Chen:

On Fri, 2022-08-05 at 18:14 +0800, Bo-Chen Chen wrote:
> From: Markus Schneider-Pargmann <msp@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@mediatek.com>
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
> Tested-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> Reviewed-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> ---

[snip]

> +
> +static int mtk_dp_train_tps_1(struct mtk_dp *mtk_dp, u8
> target_lane_count,
> +			      u8 *lane_adjust, int *status_control,
> +			      u8 *prev_lane_adjust)
> +{
> +	u8 link_status[DP_LINK_STATUS_SIZE] = {};
> +
> +	mtk_dp_training_set_scramble(mtk_dp, false);

I think this statement could be moved to mtk_dp_train_flow() before the
training loop. After this moving, mtk_dp_train_tps_1() is almost the
same as mtk_dp_train_tps_2_3(), so try to merge these two function.

> +
> +	if (*status_control == 0) {
> +		mtk_dp_pattern(mtk_dp, true, target_lane_count,
> lane_adjust);
> +		*status_control = 1;

if calling mtk_dp_pattern() directly from mtk_dp_train_flow(), we could
drop status_control.

Regards,
CK

> +	}
> +
> +	drm_dp_link_train_clock_recovery_delay(&mtk_dp->aux, mtk_dp-
> >rx_cap);
> +	drm_dp_dpcd_read_link_status(&mtk_dp->aux, link_status);
> +
> +	if (drm_dp_clock_recovery_ok(link_status,
> +				     target_lane_count)) {
> +		mtk_dp->train_info.cr_done = true;
> +		dev_dbg(mtk_dp->dev, "Link train CR pass\n");
> +		return 0;
> +	} else if (*prev_lane_adjust == link_status[4]) {
> +		if (*prev_lane_adjust &
> DP_ADJUST_VOLTAGE_SWING_LANE0_MASK) {
> +			dev_dbg(mtk_dp->dev, "Link train CQ fail\n");
> +			return -EINVAL;
> +		}
> +	} else {
> +		*prev_lane_adjust = link_status[4];
> +	}
> +	return -EAGAIN;
> +}
> +
> +static int mtk_dp_train_tps_2_3(struct mtk_dp *mtk_dp, u8
> target_linkrate,
> +				u8 target_lane_count, u8 *lane_adjust,
> +				int *status_control, u8
> *prev_lane_adjust)
> +{
> +	u8 link_status[DP_LINK_STATUS_SIZE] = {};
> +
> +	if (*status_control == 1) {
> +		mtk_dp_pattern(mtk_dp, false, target_lane_count,
> lane_adjust);
> +		*status_control = 2;
> +	}
> +
> +	drm_dp_link_train_channel_eq_delay(&mtk_dp->aux, mtk_dp-
> >rx_cap);
> +
> +	drm_dp_dpcd_read_link_status(&mtk_dp->aux, link_status);
> +
> +	if (drm_dp_channel_eq_ok(link_status, target_lane_count)) {
> +		mtk_dp->train_info.eq_done = true;
> +		dev_dbg(mtk_dp->dev, "Link train EQ pass\n");
> +		return 0;
> +	}
> +
> +	dev_dbg(mtk_dp->dev, "Link train EQ fail\n");
> +
> +	if (*prev_lane_adjust != link_status[4])
> +		*prev_lane_adjust = link_status[4];
> +
> +	return -EAGAIN;
> +}
> +
> +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 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;
> +	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 ret;
> +
> +	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)
> +			return -ENODEV;
> +
> +		if (!pass_tps1) {
> +			ret = mtk_dp_train_tps_1(mtk_dp,
> target_lane_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,
> +						   lane_adjust,
> &status_control,
> +						   &prev_lane_adjust);
> +			if (!ret) {
> +				pass_tps2_3 = true;
> +				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_DOWNSCALE_RETRY);
> +
> +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_TRAINING_PATTERN_SET,
> +			   DP_TRAINING_PATTERN_DISABLE);
> +	mtk_dp_train_set_pattern(mtk_dp, 0);
> +
> +	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;
> +}
> +