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

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Date:   Tue, 7 Jun 2022 20:55:25 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     CK Hu <ck.hu@...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 (云春峰) 
        <Chunfeng.Yun@...iatek.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, "Helge Deller" <deller@....de>,
        Jitao Shi (石记涛) 
        <jitao.shi@...iatek.com>
CC:     Markus Schneider-Pargmann <msp@...libre.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort
 driver

On Tue, 2022-06-07 at 16:12 +0800, CK Hu wrote:
> 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_start(struct mtk_dp *mtk_dp)
> > +{
> > +	int ret = 0;
> > +	u8 lane_count;
> > +	u8 link_rate;
> > +	u8 train_limit;
> > +	u8 max_link_rate;
> > +	u8 plug_wait;
> > +
> > +	for (plug_wait = 7; !mtk_dp_plug_state(mtk_dp) && plug_wait >
> > 0;
> > +	     --plug_wait)
> > +		/* Avoid short pulses on the HPD isr */
> > +		usleep_range(1000, 5000);
> > +	if (plug_wait == 0) {
> > +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_DPIDLE;
> 
> After return, mtk_dp->train_state would be set to
> MTK_DP_TRAIN_STATE_DPIDLE, so drop this.
> 

ok, I will do this.

> > +		return -ENODEV;
> > +	}
> > +
> > +	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) {
> > +			switch (link_rate) {
> > +			case MTK_DP_LINKRATE_RBR:
> > +				lane_count = lane_count / 2;
> > +				link_rate = max_link_rate;
> > +				if (lane_count == 0) {
> > +					mtk_dp->train_state =
> > +						MTK_DP_TRAIN_STATE_DPID
> > LE;
> 
> After return, mtk_dp->train_state would be set to
> MTK_DP_TRAIN_STATE_DPIDLE, so drop this.
> 
> Regards,
> CK
> 

ok.

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