linux-kernel - Re: [PATCH v16 3/8] drm/mediatek: Add MT8195 Embedded DisplayPort driver

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Message-ID: <6f067d36efffab65490348704bb892252cc400ef.camel@mediatek.com>
Date:   Tue, 9 Aug 2022 15:57:18 +0800
From:   Bo-Chen 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 v16 3/8] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

On Mon, 2022-08-08 at 13:46 +0800, CK Hu wrote:
> Hi, Bo-Chen:
> 
> On Fri, 2022-08-05 at 18:14 +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>
> > Tested-by: AngeloGioacchino Del Regno <
> > angelogioacchino.delregno@...labora.com>
> > Reviewed-by: AngeloGioacchino Del Regno <
> > angelogioacchino.delregno@...labora.com>
> > ---
> 
> [snip]
> 
> > +
> > +static irqreturn_t mtk_dp_hpd_event(int hpd, void *dev)
> > +{
> > +	struct mtk_dp *mtk_dp = dev;
> > +	struct mtk_dp_train_info *train_info = &mtk_dp->train_info;
> > +	u32 irq_status;
> > +
> > +	irq_status = mtk_dp_read(mtk_dp, MTK_DP_TOP_IRQ_STATUS);
> > +
> > +	if (!(irq_status & RGS_IRQ_STATUS_TRANSMITTER))
> > +		return IRQ_HANDLED;
> 
> If one of MTK_DP_HPD_INTERRUPT, MTK_DP_HPD_CONNECT,
> MTK_DP_HPD_DISCONNECT exist, does it imply RGS_IRQ_STATUS_TRANSMITTER
> exist? If so, I think this checking is redundant because we could
> directly check MTK_DP_HPD_INTERRUPT, MTK_DP_HPD_CONNECT,
> MTK_DP_HPD_DISCONNECT.
> 

Hello CK,

After checking with Jitao, we can remove this check and use
mtk_dp_swirq_get_clear|mtk_dp_hwirq_get_clear directly.

> > +
> > +	irq_status = mtk_dp_swirq_get_clear(mtk_dp) |
> > +		     mtk_dp_hwirq_get_clear(mtk_dp);
> > +
> > +	if (!irq_status)
> > +		return IRQ_HANDLED;
> > +
> > +	if (irq_status & MTK_DP_HPD_INTERRUPT)
> > +		train_info->hpd_inerrupt = true;
> 
> train_info->hpd_inerrupt is useless, so drop it.
> 
> > +
> > +	if (!(irq_status & MTK_DP_HPD_CONNECT ||
> > +	      irq_status & MTK_DP_HPD_DISCONNECT))
> > +		return IRQ_WAKE_THREAD;
> 
> this could be changed to
> 
> if (irq_status == MTK_DP_HPD_INTERRUPT)
> 	return IRQ_WAKE_THREAD;
> 
> But I find one problem. If irq_status == MTK_DP_HPD_INTERRUPT |
> MTK_DP_HPD_CONNECT, the thread would not be waked up. Is this what
> you
> want?
> 
> Regards,
> CK
> 

It is possible we will encounter (irq_status & MTK_DP_HPD_CONNECT) &&
(irq_status & MTK_DP_HPD_INTERRUPT)

So I will modify like this:

if (!(irq_status & MTK_DP_HPD_CONNECT ||
      irq_status & MTK_DP_HPD_DISCONNECT))
	return IRQ_WAKE_THREAD;

xxxxxx

if (irq_status & MTK_DP_HPD_INTERRUPT &&
    irq_status & MTK_DP_HPD_CONNECT)
	return IRQ_WAKE_THREAD;

return IRQ_HANDLED;

BRs,
Bo-Chen
> > +
> > +	if (!!(mtk_dp_read(mtk_dp, MTK_DP_TRANS_P0_3414) &
> > +	       HPD_DB_DP_TRANS_P0_MASK))
> > +		train_info->cable_plugged_in = true;
> > +	else
> > +		train_info->cable_plugged_in = false;
> > +
> > +	mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_PWR_STATE,
> > +			   DP_PWR_STATE_BANDGAP_TPLL_LANE,
> > +			   DP_PWR_STATE_MASK);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> 
>