linux-kernel - Re: [PATCH v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

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Date:   Wed, 15 Jun 2022 13:50:14 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Bo-Chen Chen <rex-bc.chen@...iatek.com>, <chunkuang.hu@...nel.org>,
        <p.zabel@...gutronix.de>, <daniel@...ll.ch>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <matthias.bgg@...il.com>, <deller@....de>,
        <airlied@...ux.ie>
CC:     <msp@...libre.com>, <granquet@...libre.com>,
        <jitao.shi@...iatek.com>, <wenst@...omium.org>,
        <angelogioacchino.delregno@...labora.com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-fbdev@...r.kernel.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

Hi, Bo-Chen:

On Fri, 2022-06-10 at 18:55 +0800, Bo-Chen Chen wrote:
> From: Markus Schneider-Pargmann <msp@...libre.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@...iatek.com>
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> [Bo-Chen: Cleanup the drivers and modify comments from reviewers]
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@...iatek.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.

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;
> +}