linux-kernel - Re: [RFC PATCH 06/10] usb: xhci: Add Tegra XHCI host-controller driver

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Date:	Thu, 15 May 2014 10:17:10 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Andrew Bresticker <abrestic@...omium.org>
Cc:	linux-tegra@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-usb@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [RFC PATCH 06/10] usb: xhci: Add Tegra XHCI host-controller driver

On Wednesday 14 May 2014 17:33:02 Andrew Bresticker wrote:
> +
> +int tegra_xhci_register_mbox_notifier(struct notifier_block *nb)
> +{
> +	int ret;
> +
> +	mutex_lock(&tegra_xhci_mbox_lock);
> +	ret = raw_notifier_chain_register(&tegra_xhci_mbox_notifiers, nb);
> +	mutex_unlock(&tegra_xhci_mbox_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(tegra_xhci_register_mbox_notifier);
> +
> +void tegra_xhci_unregister_mbox_notifier(struct notifier_block *nb)
> +{
> +	mutex_lock(&tegra_xhci_mbox_lock);
> +	raw_notifier_chain_unregister(&tegra_xhci_mbox_notifiers, nb);
> +	mutex_unlock(&tegra_xhci_mbox_lock);
> +}
> +EXPORT_SYMBOL(tegra_xhci_unregister_mbox_notifier);

What driver would use these?

My feeling is that if you have a mailbox that is used by multiple
drivers, you should use a proper mailbox driver to operate them,
and have the drivers register with that API instead of a custom one.

> +	/* Create child xhci-plat device */
> +	memset(xhci_resources, 0, sizeof(xhci_resources));
> +	res = platform_get_resource(to_platform_device(dev), IORESOURCE_IRQ, 0);
> +	if (!res) {
> +		dev_err(dev, "Missing XHCI IRQ\n");
> +		ret = -ENODEV;
> +		goto out;
> +	}
> +	xhci_resources[0].start = res->start;
> +	xhci_resources[0].end = res->end;
> +	xhci_resources[0].flags = res->flags;
> +	xhci_resources[0].name = res->name;
> +	res = platform_get_resource(to_platform_device(dev), IORESOURCE_MEM, 0);
> +	if (!res) {
> +		dev_err(dev, "Missing XHCI registers\n");
> +		ret = -ENODEV;
> +		goto out;
> +	}
> +	xhci_resources[1].start = res->start;
> +	xhci_resources[1].end = res->end;
> +	xhci_resources[1].flags = res->flags;
> +	xhci_resources[1].name = res->name;
> +
> +	xhci = platform_device_alloc("xhci-hcd", PLATFORM_DEVID_AUTO);
> +	if (!xhci) {
> +		dev_err(dev, "Failed to allocate XHCI host\n");
> +		ret = -ENOMEM;
> +		goto out;
> +	}

This does not feel appropriate at all: Rather than creating a child device,
you should have a specific driver that hooks into functions exported
by the xhci core. See Documentation/driver-model/design-patterns.txt

	Arnd

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