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

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Date:   Tue, 7 Jun 2022 14:44:32 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Rex-BC Chen <rex-bc.chen@...iatek.com>,
        Guillaume Ranquet <granquet@...libre.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        "Daniel Vetter" <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        "Kishon Vijay Abraham I" <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, "Helge Deller" <deller@....de>,
        Jitao shi <jitao.shi@...iatek.com>
CC:     Markus Schneider-Pargmann <msp@...libre.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-phy@...ts.infradead.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort
 driver

Hi, Rex:

On Mon, 2022-05-23 at 12:47 +0200, Guillaume Ranquet wrote:
> From: Markus Schneider-Pargmann <msp@...libre.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@...iatek.com>.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> ---

[snip]

> +
> +static int mtk_dp_train_handler(struct mtk_dp *mtk_dp)
> +{
> +	bool training_done = false;
> +	short max_retry = 50;
> +	int ret = 0;
> +
> +	do {
> +		switch (mtk_dp->train_state) {
> +		case MTK_DP_TRAIN_STATE_STARTUP:

mtk_dp->train_state is initialized as MTK_DP_TRAIN_STATE_STARTUP even
though HPD ISR does not exist. Does this mean HPD ISR is redundant? If
HPD ISR is not redundant, create a new state MTK_DP_TRAIN_STATE_NONE
for init state.

> +			mtk_dp_state_handler(mtk_dp);
> +			mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_CHECKCAP;
> +			break;
> +
> +		case MTK_DP_TRAIN_STATE_CHECKCAP:
> +			if (mtk_dp_parse_capabilities(mtk_dp)) {
> +				mtk_dp->train_info.check_cap_count = 0;
> +				mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_CHECKEDID;
> +			} else {
> +				mtk_dp->train_info.check_cap_count++;
> +
> +				if (mtk_dp->train_info.check_cap_count
> >
> +				    MTK_DP_CHECK_SINK_CAP_TIMEOUT_COUNT
> ) {
> +					mtk_dp-
> >train_info.check_cap_count = 0;
> +					mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_DPIDLE;
> +					ret = -ETIMEDOUT;
> +				}
> +			}
> +			break;
> +
> +		case MTK_DP_TRAIN_STATE_CHECKEDID:
> +			mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_TRAINING_PRE;

MTK_DP_TRAIN_STATE_CHECKEDID is a redundant state, drop it.

> +			break;
> +
> +		case MTK_DP_TRAIN_STATE_TRAINING_PRE:
> +			mtk_dp_state_handler(mtk_dp);
> +			mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_TRAINING;
> +			break;
> +
> +		case MTK_DP_TRAIN_STATE_TRAINING:
> +			ret = mtk_dp_train_start(mtk_dp);
> +			if (ret == 0) {
> +				mtk_dp_video_mute(mtk_dp, true);
> +				mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_NORMAL;
> +				mtk_dp_fec_enable(mtk_dp, mtk_dp-
> >has_fec);
> +			} else if (ret != -EAGAIN) {
> +				mtk_dp->train_state =
> MTK_DP_TRAIN_STATE_DPIDLE;
> +			}
> +			break;
> +		case MTK_DP_TRAIN_STATE_NORMAL:
> +			mtk_dp_state_handler(mtk_dp);
> +			training_done = true;
> +			break;
> +		case MTK_DP_TRAIN_STATE_DPIDLE:

When would this case happen?

Regards,
CK

> +			break;
> +		default:
> +			break;
> +		}
> +
> +		if (ret) {
> +			if (ret == -EAGAIN)
> +				continue;
> +			/*
> +			 * If we get any other error number, it doesn't
> +			 * make any sense to keep iterating.
> +			 */
> +			break;
> +		}
> +	} while (!training_done || --max_retry);
> +
> +	return ret;
> +}