linux-kernel - Re: [PATCH] drm/bridge: add support for lontium lt9211c bridge

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Message-ID: <n3hycqdiupxhfuswrhckwel5q2qc2a354t5dueoaa3x2bviuza@xgqkkhfmr5o4>
Date: Mon, 15 Sep 2025 04:19:57 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Nilesh Laad <nilesh.laad@....qualcomm.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        venkata.valluru@....qualcomm.com, jessica.zhang@....qualcomm.com,
        Yi Zhang <zhanyi@....qualcomm.com>
Subject: Re: [PATCH] drm/bridge: add support for lontium lt9211c bridge

On Thu, Sep 11, 2025 at 08:25:27PM +0530, Nilesh Laad wrote:
> From: Yi Zhang <zhanyi@....qualcomm.com>
> 
> LT9211c is a Single/Dual-Link DSI/LVDS or Single DPI input to
> Single-link/Dual-Link DSI/LVDS or Single DPI output bridge chip.
> Add support for DSI to LVDS bridge configuration.
> 
> Signed-off-by: Yi Zhang <zhanyi@....qualcomm.com>
> Signed-off-by: Nilesh Laad <nilesh.laad@....qualcomm.com>

Please send the driver together with the bindings, in one series.

The driver looks pretty similar to the existing LT9211 driver. Please
explain why you can't extend that one.

> ---
>  drivers/gpu/drm/bridge/Kconfig           |   13 +
>  drivers/gpu/drm/bridge/Makefile          |    1 +
>  drivers/gpu/drm/bridge/lontium-lt9211c.c | 1105 ++++++++++++++++++++++++++++++
>  3 files changed, 1119 insertions(+)
> 
> +	const struct reg_sequence lt9211c_tx_ssc_seq[] = {
> +		{ 0x8234, 0x00 },
> +		{ 0x856e, 0x10 },
> +		{ 0x8181, 0x15 },
> +		{ 0x871e, 0x00 },
> +		{ 0x8717, 0x02 },
> +		{ 0x8718, 0x04 },
> +		{ 0x8719, 0xd4 },
> +		{ 0x871A, 0x00 },
> +		{ 0x871B, 0x12 },
> +		{ 0x871C, 0x00 },
> +		{ 0x871D, 0x24 },
> +		{ 0x871F, 0x1c },

lowercase the hex, please.

> +		{ 0x8720, 0x00 },
> +		{ 0x8721, 0x00 },
> +		{ 0x871e, 0x02 },
> +	};
> +

[...]

> +
> +static void lt9211c_atomic_enable(struct drm_bridge *bridge,
> +				struct drm_atomic_state *state)
> +{
> +	struct lt9211c *ctx = bridge_to_lt9211c(bridge);
> +	const struct drm_bridge_state *bridge_state;
> +	const struct drm_crtc_state *crtc_state;
> +	struct drm_connector *connector;
> +	struct drm_crtc *crtc;
> +	u32 bus_flags;
> +	int ret;
> +
> +	ret = regulator_enable(ctx->vccio);
> +	if (ret) {
> +		dev_err(ctx->dev, "Failed to enable vccio: %d\n", ret);
> +		return;
> +	}
> +
> +	/* Deassert reset */
> +	gpiod_set_value(ctx->reset_gpio, 1);
> +	usleep_range(20000, 21000);	/* Very long post-reset delay. */
> +
> +	/* Get the LVDS format from the bridge state. */
> +	bridge_state = drm_atomic_get_new_bridge_state(state, bridge);
> +	bus_flags = bridge_state->output_bus_cfg.flags;
> +	ctx->de = !!(bus_flags & DRM_BUS_FLAG_DE_HIGH);
> +
> +	switch (bridge_state->output_bus_cfg.format) {
> +	case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
> +		ctx->bpp24 = false;
> +		ctx->jeida = true;
> +		break;
> +	case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
> +		ctx->bpp24 = true;
> +		ctx->jeida = true;
> +		break;
> +	case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
> +		ctx->bpp24 = true;
> +		ctx->jeida = false;
> +		break;
> +	default:
> +		/*
> +		 * Some bridges still don't set the correct
> +		 * LVDS bus format, use SPWG24 default
> +		 * format until those are fixed.
> +		 */
> +		ctx->bpp24 = true;
> +		ctx->jeida = false;
> +		dev_warn(ctx->dev,
> +			 "Unsupported LVDS bus format 0x%04x\n",
> +			 bridge_state->output_bus_cfg.format);
> +		break;
> +	}
> +
> +	/*
> +	 * Retrieve the CRTC adjusted mode. This requires a little dance to go
> +	 * from the bridge to the encoder, to the connector and to the CRTC.
> +	 */
> +	connector = drm_atomic_get_new_connector_for_encoder(state,
> +							     bridge->encoder);
> +	crtc = drm_atomic_get_new_connector_state(state, connector)->crtc;
> +	crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> +	drm_mode_copy(&ctx->mode, &crtc_state->adjusted_mode);
> +
> +	dev_dbg(ctx->dev, "width=%d,height=%d,clock=%d\n",
> +			ctx->mode.hdisplay,
> +			ctx->mode.vdisplay,
> +			ctx->mode.clock);
> +
> +	ret = lt9211c_read_chipid(ctx);
> +	if (ret)
> +		return;
> +
> +	/* Lt9211c must enable after mipi clock enable */
> +	queue_delayed_work(ctx->wq, &ctx->lt9211c_dw,
> +		msecs_to_jiffies(100));

At this point MIPI clock should be enabled.

> +
> +	dev_dbg(ctx->dev, "LT9211 enabled.\n");
> +}
> +

[...]

> +
> +MODULE_DESCRIPTION("Lontium LT9211C DSI/LVDS/DPI bridge driver");
> +MODULE_LICENSE("GPL");

Missing MODULE_AUTHOR

> 
> ---
> base-commit: f50b969bafafb2810a07f376387350c4c0d72a21
> change-id: 20250911-lt9211c-bridge-support-9209f7cc7697
> prerequisite-message-id: <20250910-add-lt9211c-bridge-v1-1-4f23740fe101@....qualcomm.com>
> prerequisite-patch-id: 79524a1aaba6b39f49603db725539cf11176820b
> 
> Best regards,
> --  
> Nilesh Laad <nilesh.laad@....qualcomm.com>
> 

-- 
With best wishes
Dmitry