linux-kernel - Re: [PATCH 2/3] drm/bridge: add lvds controller support for sam9x7

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Message-ID: <7cd4d9f9-e14a-4cd4-92f7-51c43acd23e2@kernel.org>
Date: Mon, 22 Jan 2024 16:49:06 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Dharma Balasubiramani <dharma.b@...rochip.com>,
 manikandan.m@...rochip.com, andrzej.hajda@...el.com,
 neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, airlied@...il.com, daniel@...ll.ch,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: linux4microchip@...rochip.com
Subject: Re: [PATCH 2/3] drm/bridge: add lvds controller support for sam9x7

On 22/01/2024 09:29, Dharma Balasubiramani wrote:
> Add a new LVDS controller driver for sam9x7 which does the following:
> - Prepares and enables the LVDS Peripheral clock
> - Defines its connector type as DRM_MODE_CONNECTOR_LVDS and adds itself
> to the global bridge list.
> - Identifies its output endpoint as panel and adds it to the encoder
> display pipeline
> - Enables the LVDS serializer
> 
> Signed-off-by: Manikandan Muralidharan <manikandan.m@...rochip.com>
> Signed-off-by: Dharma Balasubiramani <dharma.b@...rochip.com>
> ---

..

> +
> +static int mchp_lvds_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct mchp_lvds *lvds;
> +	struct resource *res;
> +	struct device_node *port;
> +	int ret;
> +
> +	if (!dev->of_node)
> +		return -ENODEV;
> +
> +	lvds = devm_kzalloc(&pdev->dev, sizeof(*lvds), GFP_KERNEL);
> +	if (!lvds)
> +		return -ENOMEM;
> +
> +	lvds->dev = dev;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	lvds->regs = devm_ioremap_resource(lvds->dev, res);

Why not combining these two?

> +	if (IS_ERR(lvds->regs))
> +		return PTR_ERR(lvds->regs);
> +
> +	lvds->pclk = devm_clk_get(lvds->dev, "pclk");
> +	if (IS_ERR(lvds->pclk)) {
> +		DRM_DEV_ERROR(lvds->dev, "could not get pclk_lvds\n");

Handle properly deferred probe. What's DRM wrapper over dev_err_probe()?

> +		return PTR_ERR(lvds->pclk);
> +	}
> +
> +	ret = clk_prepare(lvds->pclk);
> +	if (ret < 0) {
> +		DRM_DEV_ERROR(lvds->dev, "failed to prepare pclk_lvds\n");
> +		return ret;
> +	}
> +
> +	port = of_graph_get_remote_node(dev->of_node, 1, 0);
> +	if (!port) {
> +		DRM_DEV_ERROR(dev,
> +			      "can't find port point, please init lvds panel port!\n");
> +		return -EINVAL;
> +	}
> +
> +	lvds->panel = of_drm_find_panel(port);
> +	of_node_put(port);
> +
> +	if (IS_ERR(lvds->panel)) {
> +		DRM_DEV_ERROR(dev, "failed to find panel node\n");
> +		return -EPROBE_DEFER;

OK, that's for sure wrong. Don't print anything on deferred probe.

> +	}
> +
> +	lvds->panel_bridge = devm_drm_panel_bridge_add(dev, lvds->panel);
> +
> +	if (IS_ERR(lvds->panel_bridge))
> +		return PTR_ERR(lvds->panel_bridge);
> +
> +	lvds->bridge.of_node = dev->of_node;
> +	lvds->bridge.type = DRM_MODE_CONNECTOR_LVDS;
> +	lvds->bridge.funcs = &mchp_lvds_bridge_funcs;
> +
> +	dev_set_drvdata(dev, lvds);
> +	pm_runtime_enable(dev);
> +
> +	drm_bridge_add(&lvds->bridge);
> +
> +	return 0;
> +}
> +
> +static int mchp_lvds_remove(struct platform_device *pdev)
> +{
> +	struct mchp_lvds *lvds = platform_get_drvdata(pdev);
> +
> +	pm_runtime_disable(&pdev->dev);
> +	clk_unprepare(lvds->pclk);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id mchp_lvds_dt_ids[] = {
> +	{
> +		.compatible = "microchip,sam9x7-lvds",
> +	},
> +	{},
> +};
> +
> +struct platform_driver mchp_lvds_driver = {
> +	.probe = mchp_lvds_probe,
> +	.remove = mchp_lvds_remove,
> +	.driver = {
> +		   .name = "microchip-lvds",
> +		   .of_match_table = mchp_lvds_dt_ids,
> +	},
> +};
> +module_platform_driver(mchp_lvds_driver);
> +
> +MODULE_AUTHOR("Manikandan Muralidharan <manikandan.m@...rochip.com>");
> +MODULE_AUTHOR("Dharma Balasubiramani <dharma.b@...rochip.com>");
> +MODULE_DESCRIPTION("Low Voltage Differential Signaling Controller Driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:microchip-lvds");

You should not need MODULE_ALIAS() in normal cases. If you need it,
usually it means your device ID table is wrong (e.g. misses either
entries or MODULE_DEVICE_TABLE()). MODULE_ALIAS() is not a substitute
for incomplete ID table.


Best regards,
Krzysztof