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

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Message-ID: <61ed067bc117a67ccdf64420401605c2fadfe43a.camel@mediatek.com>
Date:   Wed, 8 Jun 2022 20:54:14 +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 Wed, 2022-06-08 at 10:44 +0800, CK Hu wrote:
> Hi, Rex:
> 
> On Tue, 2022-06-07 at 20:44 +0800, Rex-BC Chen wrote:
> > On Tue, 2022-06-07 at 14:44 +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_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.
> > > 
> > 
> > Hello CK,
> > 
> > I think we don't need MTK_DP_TRAIN_STATE_NONE.
> > Because it's "DP_TRAIN_STATE" not "DP_STATE", I think it's ok if we
> > start this state machine with "MTK_DP_TRAIN_STATE_STARTUP".
> 
> The initial state is MTK_DP_TRAIN_STATE_STARTUP, and HPD thread would
> change state from MTK_DP_TRAIN_STATE_STARTUP to
> MTK_DP_TRAIN_STATE_STARTUP, this is redundant. So drop the state
> change
> in HPD thread.
> 

ok, in edp it's redundant in mtk_dp_hpd_event_thread(), but I will add
it back in dp patch.

> > 
> > > > +			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_TIMEO
> > > > UT_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
> > 
> > Yes, if it's disconnected if we are still training for dp.
> > or failed to training min spec RBR.
> 
> I mean, every time state change to MTK_DP_TRAIN_STATE_DPIDLE, it
> would
> jump out of this loop and would not get into this loop, so this case
> would never get in. This is redundant, so remove this.
> 
> Regards,
> CK
> 

ok, I will remove it

BRs,
Bo-Chen

> > 
> > BRs,
> > Rex
> > > 
> > > > +			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;
> > > > +}
> > > 
> > > 
> > 
> > 
> 
>