Re: [PATCH v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

CK Hu
2022-07-14T07:07:00Z

Hi, Bo-Chen:

On Tue, 2022-07-12 at 19:12 +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>
> ---

[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 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,
> + &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);

train_retries and iteration_count are the same thing, so keep one and
drop another one.

Regards,
CK

> +
> + 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;
> +}
> +