linux-kernel - Re: [PATCH v13 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

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Message-ID: <d7078ff355a797081fcbd374c33fa5f4c74f4c98.camel@mediatek.com>
Date:   Thu, 7 Jul 2022 15:50:12 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Bo-Chen Chen <rex-bc.chen@...iatek.com>, <chunkuang.hu@...nel.org>,
        <p.zabel@...gutronix.de>, <daniel@...ll.ch>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <matthias.bgg@...il.com>, <deller@....de>,
        <airlied@...ux.ie>
CC:     <msp@...libre.com>, <granquet@...libre.com>,
        <jitao.shi@...iatek.com>, <wenst@...omium.org>,
        <angelogioacchino.delregno@...labora.com>,
        <liangxu.xu@...iatek.com>, <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-fbdev@...r.kernel.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v13 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

Hi, Bo-Chen:

On Fri, 2022-07-01 at 14:28 +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]

> +/*
> + * We need to handle HPD signal in eDP even though eDP is a always
> connected
> + * device. Besides connected status, there is another feature for
> HPD signal -
> + * HPD pulse: it presents an IRQ from sink devices to source devices
> (Refer to
> + * 5.1.4 of DP1.4 spec).
> + */
> +static irqreturn_t mtk_dp_hpd_isr_handler(struct mtk_dp *mtk_dp)
> +{
> +	bool connected;
> +	bool hpd_connect_sta;
> +	u32 irq_status = mtk_dp_swirq_get_clear(mtk_dp) |
> +			 mtk_dp_hwirq_get_clear(mtk_dp);
> +	struct mtk_dp_train_info *train_info = &mtk_dp->train_info;
> +
> +	if (irq_status & MTK_DP_HPD_INTERRUPT)
> +		train_info->irq_sta.hpd_inerrupt = true;
> +	if (irq_status & MTK_DP_HPD_CONNECT)
> +		hpd_connect_sta = true;
> +	if (irq_status & MTK_DP_HPD_DISCONNECT)
> +		train_info->irq_sta.hpd_disconnect = true;

hpd_disconnect is used only in this function, so let it be local
variable.

> +
> +	if (!irq_status)
> +		return IRQ_HANDLED;

Move this to top of this function.

> +
> +	connected = mtk_dp_plug_state(mtk_dp);
> +	if (connected || !train_info->cable_plugged_in)
> +		train_info->irq_sta.hpd_disconnect  = false;

The truth table of (irq_status & MTK_DP_HPD_DISCONNECT, connected,
cable_plugged_in, hpd_disconnect) is

0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 1
1 1 0 0
1 1 1 0

So the only case that hpd_disconnect is true is

(irq_status & MTK_DP_HPD_DISCONNECT) && !connected && train_info-
>cable_plugged_in)

And train_info->cable_plugged_in is the previous status. The previous
status is connected. And irq_status and connected is the new status.
The new status is disconnected.

I have a question. Why we need both irq_status and connected for new
status? I think connected is enough for new status, so we could ignore
irq_status.

Regards,
CK

> +	else if (!connected || train_info->cable_plugged_in)
> +		hpd_connect_sta = false;
> +
> +	if (!(hpd_connect_sta || train_info->irq_sta.hpd_disconnect))
> +		return IRQ_WAKE_THREAD;
> +
> +	if (hpd_connect_sta) {
> +		hpd_connect_sta = false;
> +		train_info->cable_plugged_in = true;
> +	} else {
> +		train_info->irq_sta.hpd_disconnect = false;
> +		train_info->cable_plugged_in = false;
> +	}
> +	train_info->cable_state_change = true;
> +
> +	return IRQ_WAKE_THREAD;
> +}
> +