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

[CK Hu <ck.hu@mediatek.com>]

Hi, Bo-Chen:

On Fri, 2022-07-01 at 14:28 +0800, Bo-Chen Chen wrote:
> From: Markus Schneider-Pargmann <msp@baylibre.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@mediatek.com>
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.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) {
> +		ret = -EAGAIN;
> +		goto err;
> +	}
> +
> +	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);
> +		ret = -EINVAL;
> +		goto err;
> +	}
> +
> +	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;
> +		}
> +	}

This if-else could be simplified as:

do {
	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;
} while (accessed_bytes < msg->size);

Regards,
CK

> +err:
> +	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;
> +}
> +