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

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Date:   Tue, 7 Jun 2022 20:46:31 +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 Tue, 2022-06-07 at 15:30 +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 ssize_t mtk_dp_aux_transfer(struct drm_dp_aux *mtk_aux,
> > +				   struct drm_dp_aux_msg *msg)
> > +{
> > +	struct mtk_dp *mtk_dp;
> > +	bool is_read;
> > +	u8 request;
> > +	size_t accessed_bytes = 0;
> > +	int ret = 0;
> > +
> > +	mtk_dp = container_of(mtk_aux, struct mtk_dp, aux);
> > +
> > +	if (!mtk_dp->train_info.cable_plugged_in ||
> > +	    mtk_dp->train_info.irq_status & MTK_DP_HPD_DISCONNECT) {
> > +		mtk_dp->train_state = MTK_DP_TRAIN_STATE_CHECKCAP;
> 
> Changing state here has no any effect, so drop this.
> 

ok, I will drop it.

> > +		return -EAGAIN;
> > +	}
> > +
> > +	switch (msg->request) {
> > +	case DP_AUX_I2C_MOT:
> > +	case DP_AUX_I2C_WRITE:
> > +	case DP_AUX_NATIVE_WRITE:
> > +	case DP_AUX_I2C_WRITE_STATUS_UPDATE:
> > +	case DP_AUX_I2C_WRITE_STATUS_UPDATE | DP_AUX_I2C_MOT:
> > +		request = msg->request &
> > ~DP_AUX_I2C_WRITE_STATUS_UPDATE;
> > +		is_read = false;
> > +		break;
> > +	case DP_AUX_I2C_READ:
> > +	case DP_AUX_NATIVE_READ:
> > +	case DP_AUX_I2C_READ | DP_AUX_I2C_MOT:
> > +		request = msg->request;
> > +		is_read = true;
> > +		break;
> > +	default:
> > +		drm_err(mtk_aux->drm_dev, "invalid aux cmd = %d\n",
> > +			msg->request);
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (msg->size == 0) {
> > +		ret = mtk_dp_aux_do_transfer(mtk_dp, is_read, request,
> > +					     msg->address +
> > accessed_bytes,
> > +					     msg->buffer +
> > accessed_bytes, 0);
> > +	} else {
> > +		while (accessed_bytes < msg->size) {
> > +			size_t to_access =
> > +				min_t(size_t, DP_AUX_MAX_PAYLOAD_BYTES,
> > +				      msg->size - accessed_bytes);
> > +
> > +			ret = mtk_dp_aux_do_transfer(mtk_dp,
> > +						     is_read, request,
> > +							 msg->address +
> > accessed_bytes,
> > +							 msg->buffer +
> > accessed_bytes,
> > +							 to_access);
> > +
> > +			if (ret) {
> > +				drm_info(mtk_dp->drm_dev,
> > +					 "Failed to do AUX transfer:
> > %d\n", ret);
> > +				break;
> > +			}
> > +			accessed_bytes += to_access;
> > +		}
> > +	}
> > +
> > +	if (ret) {
> > +		msg->reply = DP_AUX_NATIVE_REPLY_NACK |
> > DP_AUX_I2C_REPLY_NACK;
> > +		return ret;
> > +	}
> > +
> > +	msg->reply = DP_AUX_NATIVE_REPLY_ACK | DP_AUX_I2C_REPLY_ACK;
> > +	return msg->size;
> > +}
> 
>