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

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Date:   Tue, 7 Jun 2022 15:30:20 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Rex-BC Chen <rex-bc.chen@...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 <chunfeng.yun@...iatek.com>,
        "Kishon Vijay Abraham I" <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, "Helge Deller" <deller@....de>,
        Jitao shi <jitao.shi@...iatek.com>
CC:     Markus Schneider-Pargmann <msp@...libre.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-phy@...ts.infradead.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort
 driver

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.

> +		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;
> +}