linux-kernel - Re: [PATCH v4 20/36] media: imx: Add CSI subdev driver

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Date:   Thu, 16 Feb 2017 11:52:06 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com, mchehab@...nel.org,
        hverkuil@...all.nl, nick@...anahar.org, markus.heiser@...marIT.de,
        p.zabel@...gutronix.de, laurent.pinchart+renesas@...asonboard.com,
        bparrot@...com, geert@...ux-m68k.org, arnd@...db.de,
        sudipm.mukherjee@...il.com, minghsiu.tsai@...iatek.com,
        tiffany.lin@...iatek.com, jean-christophe.trotin@...com,
        horms+renesas@...ge.net.au, niklas.soderlund+renesas@...natech.se,
        robert.jarzmik@...e.fr, songjun.wu@...rochip.com,
        andrew-ct.chen@...iatek.com, gregkh@...uxfoundation.org,
        shuah@...nel.org, sakari.ailus@...ux.intel.com, pavel@....cz,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v4 20/36] media: imx: Add CSI subdev driver

On Wed, Feb 15, 2017 at 06:19:22PM -0800, Steve Longerbeam wrote:
> +static const struct platform_device_id imx_csi_ids[] = {
> +	{ .name = "imx-ipuv3-csi" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(platform, imx_csi_ids);
> +
> +static struct platform_driver imx_csi_driver = {
> +	.probe = imx_csi_probe,
> +	.remove = imx_csi_remove,
> +	.id_table = imx_csi_ids,
> +	.driver = {
> +		.name = "imx-ipuv3-csi",
> +	},
> +};
> +module_platform_driver(imx_csi_driver);
> +
> +MODULE_DESCRIPTION("i.MX CSI subdev driver");
> +MODULE_AUTHOR("Steve Longerbeam <steve_longerbeam@...tor.com>");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:imx-ipuv3-csi");

Just a reminder that automatic module loading of this is completely
broken right now (not your problem) due to this stupid idea in the
IPUv3 code:

		if (!ret)
			ret = platform_device_add(pdev);
		if (ret) {
			platform_device_put(pdev);
			goto err_register;
		}

		/*
		 * Set of_node only after calling platform_device_add. Otherwise
		 * the platform:imx-ipuv3-crtc modalias won't be used.
		 */
		pdev->dev.of_node = of_node;

setting pdev->dev.of_node changes the modalias exported to userspace,
so udev sees a DT based modalias, which causes it to totally miss any
driver using a non-DT based modalias.

The IPUv3 code needs fixing, not only for imx-media-csi, but also for
imx-ipuv3-crtc too, because that module will also suffer the same
issue.

The only solution is... don't fsck with dev->of_node assignment.  In
this case, it's probably much better to pass it in via platform data.
If you then absolutely must have dev->of_node, doing it in the driver
means that you avoid the modalias mess before the appropriate driver
is loaded.  However, that's still not a nice solution because the
modalias file still ends up randomly changing its contents.

As I say, not _your_ problem, but it's still a problem that needs
solving, and I don't want it forgotten about.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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