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

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Date:   Wed, 8 Jun 2022 18:26:33 +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 15:47 +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_hpd_sink_event(struct mtk_dp *mtk_dp)
> > +{
> > +	ssize_t ret;
> > +	u8 sink_count;
> > +	bool locked;
> > +	u8 link_status[DP_LINK_STATUS_SIZE] = {};
> > +	u32 sink_count_reg = DP_SINK_COUNT_ESI;
> > +	u32 link_status_reg = DP_LANE0_1_STATUS;
> > +
> > +	ret = drm_dp_dpcd_readb(&mtk_dp->aux, sink_count_reg,
> > &sink_count);
> > +	if (ret < 0) {
> > +		drm_err(mtk_dp->drm_dev, "Read sink count failed:
> > %ld\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	ret = drm_dp_dpcd_read(&mtk_dp->aux, link_status_reg,
> > link_status,
> > +			       sizeof(link_status));
> > +	if (!ret) {
> > +		drm_err(mtk_dp->drm_dev, "Read link status failed:
> > %ld\n",
> > +			ret);
> > +		return ret;
> > +	}
> > +
> > +	locked = drm_dp_channel_eq_ok(link_status,
> > +				      mtk_dp->train_info.lane_count);
> > +	if (!locked && mtk_dp->train_state >
> > MTK_DP_TRAIN_STATE_TRAINING_PRE)
> 
> Before enter this function, mtk_dp->train_state is set to
> MTK_DP_TRAIN_STATE_STARTUP, so this never happen, drop this.
> 

The interrupt from sink device could come any time. Why it's
impossible?

> > +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_TRAINING_PRE;
> > +
> > +	if (link_status[1] & DP_REMOTE_CONTROL_COMMAND_PENDING)
> > +		drm_dp_dpcd_writeb(&mtk_dp->aux,
> > DP_DEVICE_SERVICE_IRQ_VECTOR,
> > +				   DP_REMOTE_CONTROL_COMMAND_PENDING);
> > +
> > +	if (DP_GET_SINK_COUNT(sink_count) &&
> > +	    (link_status[2] & DP_DOWNSTREAM_PORT_STATUS_CHANGED)) {
> > +		mtk_dp->train_info.check_cap_count = 0;
> > +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_CHECKEDID;
> 
> Why change state from MTK_DP_TRAIN_STATE_STARTUP to
> MTK_DP_TRAIN_STATE_CHECKEDID? In mtk_dp_train_handler(),
> mtk_dp_parse_capabilities() is true then change to
> MTK_DP_TRAIN_STATE_CHECKEDID. Give a reason why these two are
> different.
> 
> Regards,
> CK
> 

I will drop this and drop state of MTK_DP_TRAIN_STATE_CHECKEDID.
MTK_DP_TRAIN_STATE_CHECKEDID is only used for audio.
We can check enable status in another place.

BRs,
Bo-Chen

> > +		msleep(20);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> 
>