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

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Date:	Fri, 18 Sep 2015 16:56:32 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-kernel@...r.kernel.org" <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" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"devicetree@...r.kernel.org" <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 17 September 2015 at 17:52, Alan Stern <stern@...land.harvard.edu> wrote:
> 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?

That seems to work, thanks for the idea!

Regards,

Tomeu

> Alan Stern
>
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