linux-kernel - Re: [PATCH v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

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Date:   Wed, 15 Jun 2022 11:06:45 +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>,
        <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 v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

Hi, Bo-Chen:

On Fri, 2022-06-10 at 18:55 +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>
> [Bo-Chen: Cleanup the drivers and modify comments from reviewers]
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@...iatek.com>
> ---

[snip]

> +
> +static int mtk_dp_parse_capabilities(struct mtk_dp *mtk_dp)
> +{
> +	u8 val;
> +	struct mtk_dp_train_info *train_info = &mtk_dp->train_info;
> +
> +	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_SET_POWER,
> DP_SET_POWER_D0);
> +	usleep_range(2000, 5000);
> +
> +	drm_dp_read_dpcd_caps(&mtk_dp->aux, mtk_dp->rx_cap);
> +
> +	mtk_dp->rx_cap[DP_TRAINING_AUX_RD_INTERVAL] &=
> DP_TRAINING_AUX_RD_MASK;
> +
> +	train_info->link_rate = min_t(int, mtk_dp->max_linkrate,
> +				      mtk_dp->rx_cap[mtk_dp-
> >max_linkrate]);
> +	train_info->lane_count = min_t(int, mtk_dp->max_lanes,
> +				       drm_dp_max_lane_count(mtk_dp-
> >rx_cap));
> +
> +	train_info->tps3 = drm_dp_tps3_supported(mtk_dp->rx_cap);
> +	train_info->tps4 = drm_dp_tps4_supported(mtk_dp->rx_cap);
> +
> +	train_info->sink_ssc = !!(mtk_dp->rx_cap[DP_MAX_DOWNSPREAD] &
> +				  DP_MAX_DOWNSPREAD_0_5);

I think this is redundant because next statement would set sink_scc to
false.

Regards,
CK

> +
> +	train_info->sink_ssc = false;
> +
> +	drm_dp_dpcd_readb(&mtk_dp->aux, DP_MSTM_CAP, &val);
> +	if (val & DP_MST_CAP) {
> +		/* Clear DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0 */
> +		drm_dp_dpcd_readb(&mtk_dp->aux,
> +				  DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0,
> &val);
> +		if (val)
> +			drm_dp_dpcd_writeb(&mtk_dp->aux,
> +					   DP_DEVICE_SERVICE_IRQ_VECTOR
> _ESI0,
> +					   val);
> +	}
> +
> +	return 0;
> +}