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

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Date:   Thu, 14 Jul 2022 14:51:47 +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>,
        <liangxu.xu@...iatek.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 v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

Hi, Bo-Chen:

On Tue, 2022-07-12 at 19:12 +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>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@...iatek.com>
> ---

[snip]

> +static int mtk_dp_train_tps_2_3(struct mtk_dp *mtk_dp, u8
> target_linkrate,
> +				u8 target_lane_count, int
> *iteration_count,
> +				u8 *lane_adjust,  int *status_control,
> +				u8 *prev_lane_adjust)
> +{
> +	u8 val;
> +	u8 link_status[DP_LINK_STATUS_SIZE] = {};
> +
> +	if (*status_control == 1) {
> +		if (mtk_dp->train_info.tps4) {
> +			mtk_dp_train_set_pattern(mtk_dp, 4);
> +			val = DP_TRAINING_PATTERN_4;
> +		} else if (mtk_dp->train_info.tps3) {
> +			mtk_dp_train_set_pattern(mtk_dp, 3);
> +			val = DP_LINK_SCRAMBLING_DISABLE |
> +				DP_TRAINING_PATTERN_3;
> +		} else {
> +			mtk_dp_train_set_pattern(mtk_dp, 2);
> +			val = DP_LINK_SCRAMBLING_DISABLE |
> +				DP_TRAINING_PATTERN_2;
> +		}
> +		drm_dp_dpcd_writeb(&mtk_dp->aux,
> +				   DP_TRAINING_PATTERN_SET, val);
> +		drm_dp_dpcd_read(&mtk_dp->aux,
> +				 DP_ADJUST_REQUEST_LANE0_1,
> lane_adjust,
> +				 sizeof(*lane_adjust) * 2);
> +
> +		mtk_dp_train_update_swing_pre(mtk_dp,
> +					      target_lane_count,
> lane_adjust);
> +		*status_control = 2;
> +		(*iteration_count)++;
> +	}
> +
> +	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_clock_recovery_ok(link_status, target_lane_count)) 

I think this checking is redundant. I think we could just keep
drm_dp_channel_eq_ok() and drop drm_dp_clock_recovery_ok() here because
if drm_dp_clock_recovery_ok() fail, it imply that
drm_dp_channel_eq_ok() would fail. So just check drm_dp_channel_eq_ok()
is enough.

Regards,
CK

> {
> +		mtk_dp->train_info.cr_done = false;
> +		mtk_dp->train_info.eq_done = false;
> +		dev_dbg(mtk_dp->dev, "Link train EQ fail\n");
> +		return -EINVAL;
> +	}
> +
> +	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;
> +	}
> +
> +	if (*prev_lane_adjust == link_status[4])
> +		(*iteration_count)++;
> +	else
> +		*prev_lane_adjust = link_status[4];
> +
> +	return -EAGAIN;
> +}
> +