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

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Date:   Wed, 8 Jun 2022 10:23:08 +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 (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

Hi, Rex:

On Tue, 2022-06-07 at 20:24 +0800, Rex-BC Chen wrote:
> On Tue, 2022-06-07 at 14:21 +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 irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
> > > +{
> > > +	struct mtk_dp *mtk_dp = dev;
> > > +	int event;
> > > +	u8 buf[DP_RECEIVER_CAP_SIZE] = {};
> > > +
> > > +	event = mtk_dp_plug_state(mtk_dp) ? connector_status_connected
> > > :
> > > +						  connector_status_disc
> > > onnected;
> > > +
> > > +	if (event < 0)
> > 
> > event is always > 0, isn't it?
> > 
> 
> Hello CK,
> 
> ok, I will move this to dp patch.
> 
> > > +		return IRQ_HANDLED;
> > > +
> > > +	if (mtk_dp->drm_dev) {
> > > +		dev_info(mtk_dp->dev, "drm_helper_hpd_irq_event\n");
> > > +		drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
> > 
> > I think this ISR would come once. If bridge has not attached, the
> > drm
> > core would lost this event. Maybe you should enable eDP hardware
> > after
> > bridge attached or send this event when attached.
> > 
> 
> for edp patch, I will move it to (mtk_dp_bridge_attach).
> for dp patch, I will add it back.

I find out that mtk_dp_poweron() is in top of mtk_dp_bridge_attach().
If move mtk_dp_poweron() to bottom of mtk_dp_bridge_attach(), mtk_dp-
>drm_dev would not be NULL here. So we could drop this checking.

> 
> > > +	}
> > > +
> > > +	if (mtk_dp->train_info.cable_state_change) {
> > 
> > Executing this thread imply cable_state_change = true, so drop
> > cable_state_change.
> > 
> 
> In mtk_dp_hpd_isr_handler(), there is another irq
> "MTK_DP_HPD_INTERRUPT" which means the sink devices give a interrupt
> to
> source device. it's not about connected status, so I think we still
> need this.

In bottom of mtk_dp_hpd_isr_handler(), the code is:

+	train_info->cable_state_change = true;
+
+	return IRQ_WAKE_THREAD;

This thread is called only when return IRQ_WAKE_THREAD, and before
return IRQ_WAKE_THREAD, train_info->cable_state_change is always set to
true. So in this thread, train_info->cable_state_change must be true.

Regards,
CK

> 
> > > +		mtk_dp->train_info.cable_state_change = false;
> > > +
> > > +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_STARTUP;
> > > +
> > > +		if (!mtk_dp->train_info.cable_plugged_in ||
> > > +		    !mtk_dp_plug_state(mtk_dp)) {
> > 
> > I do not like two variable to present one thing. If
> > 
> > mtk_dp->train_info.cable_plugged_in = false
> > and
> > mtk_dp_plug_state(mtk_dp) = ture
> > 
> > What does this mean? I think this mean 'now' is connected because
> > cable_plugged_in is old information and mtk_dp_plug_state() is
> > current
> > information.
> > 
> > But I would like to keep cable_plugged_in and drop
> > mtk_dp_plug_state()
> > because cable_plugged_in would be changed in isr and it would be
> > the
> > same as mtk_dp_plug_state().
> > 
> > Regards,
> > CK
> > 
> 
> ok, I will drop this.
> 
> BRs,
> Rex
> 
> > > +			mtk_dp_video_mute(mtk_dp, true);
> > > +
> > > +			mtk_dp_initialize_priv_data(mtk_dp);
> > > +			mtk_dp_set_idle_pattern(mtk_dp, true);
> > > +			if (mtk_dp->has_fec)
> > > +				mtk_dp_fec_enable(mtk_dp, false);
> > > +
> > > +			mtk_dp_update_bits(mtk_dp,
> > > MTK_DP_TOP_PWR_STATE,
> > > +					   DP_PWR_STATE_BANDGAP_TPLL,
> > > +					   DP_PWR_STATE_MASK);
> > > +		} else {
> > > +			mtk_dp_update_bits(mtk_dp,
> > > MTK_DP_TOP_PWR_STATE,
> > > +					   DP_PWR_STATE_BANDGAP_TPLL_LA
> > > NE,
> > > +					   DP_PWR_STATE_MASK);
> > > +			drm_dp_read_dpcd_caps(&mtk_dp->aux, buf);
> > > +			mtk_dp->train_info.link_rate =
> > > +				min_t(int, mtk_dp->max_linkrate,
> > > +				      buf[mtk_dp->max_linkrate]);
> > > +			mtk_dp->train_info.lane_count =
> > > +				min_t(int, mtk_dp->max_lanes,
> > > +				      drm_dp_max_lane_count(buf));
> > > +		}
> > > +	}
> > > +
> > > +	if (mtk_dp->train_info.irq_status & MTK_DP_HPD_INTERRUPT) {
> > > +		dev_dbg(mtk_dp->dev, "MTK_DP_HPD_INTERRUPT\n");
> > > +		mtk_dp->train_info.irq_status &= ~MTK_DP_HPD_INTERRUPT;
> > > +		mtk_dp_hpd_sink_event(mtk_dp);
> > > +	}
> > > +
> > > +	return IRQ_HANDLED;
> > > +}
> > > +
> > 
> > 
> 
>