Re: [PATCH v12 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

From: CK Hu <ck.hu@mediatek.com>
To: Bo-Chen Chen <rex-bc.chen@mediatek.com>,
	<chunkuang.hu@kernel.org>, <p.zabel@pengutronix.de>,
	<daniel@ffwll.ch>, <robh+dt@kernel.org>,
	<krzysztof.kozlowski+dt@linaro.org>, <mripard@kernel.org>,
	<tzimmermann@suse.de>, <matthias.bgg@gmail.com>, <deller@gmx.de>,
	<airlied@linux.ie>
Cc: <msp@baylibre.com>, <granquet@baylibre.com>,
	<jitao.shi@mediatek.com>, <wenst@chromium.org>,
	<angelogioacchino.delregno@collabora.com>,
	<dri-devel@lists.freedesktop.org>,
	<linux-mediatek@lists.infradead.org>,
	<devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-fbdev@vger.kernel.org>,
	<Project_Global_Chrome_Upstream_Group@mediatek.com>
Subject: Re: [PATCH v12 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver
Date: Wed, 29 Jun 2022 11:51:24 +0800	[thread overview]
Message-ID: <fcb60f65a30721970b7647633feea4f1df1bf774.camel@mediatek.com> (raw)
In-Reply-To: <20220627080341.5087-6-rex-bc.chen@mediatek.com>

Hi, Bo-Chen:

On Mon, 2022-06-27 at 16:03 +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>
> [Bo-Chen: Cleanup the drivers and modify comments from reviewers]
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
> ---

[snip]

> +
> +static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
> +{
> +	struct mtk_dp *mtk_dp = dev;
> +	u8 buf[DP_RECEIVER_CAP_SIZE] = {};
> +
> +	if (mtk_dp->train_info.cable_state_change) {
> +		mtk_dp->train_info.cable_state_change = false;
> +
> +		mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_PWR_STATE,
> +				   DP_PWR_STATE_BANDGAP_TPLL_LANE,
> +				   DP_PWR_STATE_MASK);
> +		drm_dp_read_dpcd_caps(&mtk_dp->aux, buf);
> +		mtk_dp->train_info.link_rate =
> +			min_t(int, mtk_dp->max_linkrate,
> +			      buf[mtk_dp->max_linkrate]);
> +		mtk_dp->train_info.lane_count =
> +			min_t(int, mtk_dp->max_lanes,
> +			      drm_dp_max_lane_count(buf));

If the state_change is unplug, why do you modify link_rate and
lane_count?
If the state_change is plug, there is a training flow to decide
link_rate and lane_count. I think the training flow is correct and any
modification here is redundant.

Regards,
CK

> +	}
> +
> +	if (mtk_dp->train_info.irq_sta.hpd_inerrupt) {
> +		dev_dbg(mtk_dp->dev, "MTK_DP_HPD_INTERRUPT\n");
> +		mtk_dp->train_info.irq_sta.hpd_inerrupt = false;
> +		mtk_dp_hpd_sink_event(mtk_dp);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +