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

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Message-ID: <c70db24fb66f844a2b53c229fff6e943e99398db.camel@mediatek.com>
Date:   Tue, 26 Jul 2022 18:06:50 +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 Tue, 2022-07-26 at 17:34 +0800, CK Hu wrote:
> On Tue, 2022-07-26 at 14:42 +0800, Rex-BC Chen wrote:
> > On Mon, 2022-07-25 at 17:16 +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_training(struct mtk_dp *mtk_dp)
> > > > +{
> > > > +	short max_retry = 50;
> > > > +	int ret;
> > > > +
> > > > +	do {
> > > > +		ret = mtk_dp_train_start(mtk_dp);
> > > > +		if (!ret)
> > > > +			break;
> > > > +		else if (ret != -EAGAIN)
> > > > +			return ret;
> > > > +	} while (--max_retry);
> > > 
> > > mtk_dp_train_start() would never return -EAGAIN, so drop this
> > > while
> > > loop.
> > > 
> > > Regards,
> > > CK
> > > 
> > 
> > Hello CK,
> > 
> > the function will not return -EAGAIN, but we still want to retry 50
> > times if mtk_dp_train_start() is failed. If we retry 50 times and
> > it
> > is
> > still failed. We can confirm there are some issues for the device.
> > 
> > I will remove the else if of -EAGAIN and keep th while loop.
> 
> In this version, it never retry. And I believe you've tested this no-
> retry version. If this no-retry version works fine, why do you insist
> on retry? If you really need retry, merge this retry into
> mtk_dp_train_start() because mtk_dp_train_start() have already retry.
> 
> Regards,
> CK
> 

Hello Ck,

There are many different devices we are not testing for DP devices.
I think we need to keep this.
This retry is for restart with init state.

I think it's better to keep it here and it's more clear.

I will remain the comments above, and I think it's enough.

BRs,
Bo-Chen

> > 
> > BRs,
> > Bo-Chen
> > > > 
> > > > +	if (!max_retry)
> > > > +		return -ETIMEDOUT;
> > > > +
> > > > +	ret = mtk_dp_video_config(mtk_dp);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +	mtk_dp_video_enable(mtk_dp, true);
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > 
> > > 
> > 
> > 
> 
>