linux-kernel - Re: [PATCH v5 01/23] driver core: Add pre_probe callback to bus

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Date:	Thu, 17 Sep 2015 11:52:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
cc:	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	<linux-arm-kernel@...ts.infradead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	<devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	<linux-acpi@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v5 01/23] driver core: Add pre_probe callback to bus_type

On Thu, 17 Sep 2015, Tomeu Vizoso wrote:

> Some buses (eg. AMBA) need access to some HW resources (it may need a
> clock to be enabled so a device ID can be read) before a device can be
> matched to a driver.
> 
> The pre_probe callback allows the device-driver core to request the bus
> to perform this initialization and can defer the probe if any of the
> resources needed are missing.
> 
> This gives us more flexibility when setting the order in which devices
> are probed because the resources needed to get the matching information
> don't need to be available by the time that the bus devices are
> registered.

Can't the subsystem do this itself in its matching routine?

Alan Stern

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