linux-kernel - RE: Q: Kconfig option VIRT_TO

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Message-ID: <ADE657CA350FB648AAC2C43247A983F00206B258868B@AUSP01VMBX24.collaborationhost.net>
Date:	Mon, 12 Nov 2012 17:13:52 -0600
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: RE: Q: Kconfig option VIRT_TO_BUS

On Monday, November 12, 2012 11:41 AM, Bjorn Helgaas wrote:
> On Mon, Nov 12, 2012 at 9:18 AM, H Hartley Sweeten wrote:
>> Does anyone know what the Kconfig option VIRT_TO_BUS does?
>> There are a number of "depends on" that option but it does not
>> seem to directly enable any code in the kernel.
>
> virt_to_bus() is a deprecated interface for converting a kernel
> virtual address to a bus address.  It's deprecated because it's
> impossible to implement correctly when there are multiple bus address
> spaces, because you don't know which bus address space the caller has
> in mind.

Thanks for the info.

So if a driver does not use virt_to_bus() then the "depends on VIRT_TO_BUS" 
is not necessary. Correct?

Thanks,
Hartley
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