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SubjectRe: [PATCH v13 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver
From
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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;
> +}
> +

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