linux-kernel - Re: [PATCH 05/16] drivers/fsi: Add fake master driver

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Date:   Wed, 7 Dec 2016 12:09:05 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Chris Bostic <christopher.lee.bostic@...il.com>
Cc:     robh+dt@...nel.org, linux@...linux.org.uk,
        gregkh@...uxfoundation.org, sre@...nel.org,
        mturquette@...libre.com, geert+renesas@...der.be,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Jeremy Kerr <jk@...abs.org>, joel@....id.au,
        linux-kernel@...r.kernel.org, andrew@...id.au,
        alistair@...ple.id.au, benh@...nel.crashing.org,
        Chris Bostic <cbostic@...ibm.com>
Subject: Re: [PATCH 05/16] drivers/fsi: Add fake master driver

On Tue, Dec 06, 2016 at 06:14:26PM -0600, Chris Bostic wrote:
> From: Jeremy Kerr <jk@...abs.org>
> 
> For debugging, add a fake master driver, that only supports reads,
> returning a fixed set of data.

> +config FSI_MASTER_FAKE
> +	tristate "Fake FSI master"
> +	depends on FSI
> +	---help---
> +	This option enables a fake FSI master driver for debugging.
> +endif

> +static const struct of_device_id fsi_master_fake_match[] = {
> +	{ .compatible = "ibm,fsi-master-fake" },
> +	{ },
> +};

NAK.

DT should be treated as an ABI, and should describe the HW explicitly.
This makes no sense. This is also missing a binding document.

Have your module take a module parameter allowing you to bind it to
arbitrary devices, or do something like what PCI does where you can
bind/unbind arbitrary drivers to devices using sysfs.

> +
> +static struct platform_driver fsi_master_fake_driver = {
> +	.driver = {
> +		.name		= "fsi-master-fake",
> +		.of_match_table	= fsi_master_fake_match,
> +	},
> +	.probe	= fsi_master_fake_probe,
> +};
> +
> +static int __init fsi_master_fake_init(void)
> +{
> +	struct device_node *np;
> +
> +	platform_driver_register(&fsi_master_fake_driver);
> +
> +	for_each_compatible_node(np, NULL, "ibm,fsi-master-fake")
> +		of_platform_device_create(np, NULL, NULL);

As a general note, please use for_each_matching_node in situations like
this. That way you can reuse your existing of_device_id table, and not
reproduce the string.

That said, this is not necessary. The platform driver has an
of_match_table, so presumes the parent bus registers children, and hence
they should already have platform devices.

Thanks,
Mark.