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

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Date:   Wed, 15 Jun 2022 14:52:25 +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_start(struct mtk_dp *mtk_dp)
> +{
> +	int ret = 0;
> +	u8 lane_count;
> +	u8 link_rate;
> +	u8 train_limit;
> +	u8 max_link_rate;
> +
> +	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) {

When mtk_dp_train_flow() return 0, it imply train_info.cr_done is true,
isn't it?

> +			switch (link_rate) {
> +			case MTK_DP_LINKRATE_RBR:
> +				lane_count = lane_count / 2;
> +				link_rate = max_link_rate;
> +				if (lane_count == 0)
> +					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) {

When mtk_dp_train_flow() return 0, it imply train_info.eq_done is true,
isn't it?

Regards,
CK

> +			if (lane_count == 0)
> +				return -EIO;
> +
> +			lane_count /= 2;
> +		} else {
> +			break;
> +		}
> +	}
> +
> +	if (train_limit == 0)
> +		return -ETIMEDOUT;
> +
> +	return 0;
> +}