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

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Date:   Thu, 14 Jul 2022 17:09:22 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     CK Hu <ck.hu@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "mripard@...nel.org" <mripard@...nel.org>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "deller@....de" <deller@....de>,
        "airlied@...ux.ie" <airlied@...ux.ie>
CC:     "msp@...libre.com" <msp@...libre.com>,
        "granquet@...libre.com" <granquet@...libre.com>,
        Jitao Shi (石记涛) 
        <jitao.shi@...iatek.com>,
        "wenst@...omium.org" <wenst@...omium.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        LiangXu Xu (徐亮) 
        <LiangXu.Xu@...iatek.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-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

On Thu, 2022-07-14 at 14:51 +0800, CK Hu wrote:
> 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;
> > +	}
> > +

Hello CK,

do you mean like this?
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;
} else {
  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;
}

BRs,
Bo-Chen

> > +	if (*prev_lane_adjust == link_status[4])
> > +		(*iteration_count)++;
> > +	else
> > +		*prev_lane_adjust = link_status[4];
> > +
> > +	return -EAGAIN;
> > +}
> > +
> 
>