Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort driver

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

Hi, Rex:

On Mon, 2022-05-23 at 12:47 +0200, Guillaume Ranquet wrote:
> From: Markus Schneider-Pargmann <msp@baylibre.com>
> 
> This patch adds a 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
> Jason-JH.Lin <jason-jh.lin@mediatek.com>.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> ---

[snip]

> +
> +static int mtk_dp_train_start(struct mtk_dp *mtk_dp)
> +{
> +	int ret = 0;
> +	u8 lane_count;
> +	u8 link_rate;
> +	u8 train_limit;
> +	u8 max_link_rate;
> +	u8 plug_wait;
> +
> +	for (plug_wait = 7; !mtk_dp_plug_state(mtk_dp) && plug_wait >
> 0;
> +	     --plug_wait)
> +		/* Avoid short pulses on the HPD isr */
> +		usleep_range(1000, 5000);
> +	if (plug_wait == 0) {
> +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_DPIDLE;

After return, mtk_dp->train_state would be set to
MTK_DP_TRAIN_STATE_DPIDLE, so drop this.

> +		return -ENODEV;
> +	}
> +
> +	link_rate = mtk_dp->rx_cap[1];
> +	lane_count = mtk_dp->rx_cap[2] & 0x1F;
> +
> +	mtk_dp->train_info.link_rate = min(mtk_dp->max_linkrate,
> link_rate);
> +	mtk_dp->train_info.lane_count = min(mtk_dp->max_lanes,
> lane_count);
> +	link_rate = mtk_dp->train_info.link_rate;
> +	lane_count = mtk_dp->train_info.lane_count;
> +
> +	switch (link_rate) {
> +	case MTK_DP_LINKRATE_RBR:
> +	case MTK_DP_LINKRATE_HBR:
> +	case MTK_DP_LINKRATE_HBR2:
> +	case MTK_DP_LINKRATE_HBR25:
> +	case MTK_DP_LINKRATE_HBR3:
> +		break;
> +	default:
> +		mtk_dp->train_info.link_rate = MTK_DP_LINKRATE_HBR3;
> +		break;
> +	};
> +
> +	max_link_rate = link_rate;
> +	for (train_limit = 6; train_limit > 0; train_limit--) {
> +		mtk_dp->train_info.cr_done = false;
> +		mtk_dp->train_info.eq_done = false;
> +
> +		mtk_dp_train_change_mode(mtk_dp);
> +		ret = mtk_dp_train_flow(mtk_dp, link_rate, lane_count);
> +		if (ret)
> +			return ret;
> +
> +		if (!mtk_dp->train_info.cr_done) {
> +			switch (link_rate) {
> +			case MTK_DP_LINKRATE_RBR:
> +				lane_count = lane_count / 2;
> +				link_rate = max_link_rate;
> +				if (lane_count == 0) {
> +					mtk_dp->train_state =
> +						MTK_DP_TRAIN_STATE_DPID
> LE;

After return, mtk_dp->train_state would be set to
MTK_DP_TRAIN_STATE_DPIDLE, so drop this.

Regards,
CK

> +					return -EIO;
> +				}
> +				break;
> +			case MTK_DP_LINKRATE_HBR:
> +				link_rate = MTK_DP_LINKRATE_RBR;
> +				break;
> +			case MTK_DP_LINKRATE_HBR2:
> +				link_rate = MTK_DP_LINKRATE_HBR;
> +				break;
> +			case MTK_DP_LINKRATE_HBR3:
> +				link_rate = MTK_DP_LINKRATE_HBR2;
> +				break;
> +			default:
> +				return -EINVAL;
> +			};
> +		} else if (!mtk_dp->train_info.eq_done) {
> +			if (lane_count == 0)
> +				return -EIO;
> +
> +			lane_count /= 2;
> +		} else {
> +			break;
> +		}
> +	}
> +
> +	if (train_limit == 0)
> +		return -ETIMEDOUT;
> +
> +	return 0;
> +}
> +