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

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Message-ID: <CAL1qeaHm7U2NVDeVZS-Tiz5ntkk4c13RR_1ws9MTYGGoGCOB5A@mail.gmail.com>
Date:	Thu, 15 May 2014 13:18:22 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	devicetree@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.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

Arnd,

On Thu, May 15, 2014 at 1:17 AM, Arnd Bergmann <arnd@...db.de> wrote:
> 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?

It's used by just this driver (the host) and the PHY driver (next
patch in series).

> 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.

Ok, will do.

>> +     /* 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

This is how DWC3, currently the only in-tree non-PCI XHCI host driver,
is structured - see drivers/usb/dwc3/host.c.  The recently proposed
Armada XHCI driver [1] just adds clock support and a hook in
xhci-plat's probe() to do the platform-specific initialization.
Tegra's XHCI driver initialization is quite a bit more complicated,
mainly due to the need for external firmware and specific ordering
(e.g. firmware messages should only be enabled after the HCD is
created).  I could do away with the xhci-plat sub-device and just
create a Tegra hc_driver, but it seems silly to have three XHCI
platform drivers structured in three different ways.  USB folks, do
you have an opinion on how this should be done?

[1] https://lkml.org/lkml/2014/5/15/208

Thanks,
Andrew
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