linux-kernel - Re: Q: Kconfig option VIRT_TO

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Message-ID: <CAErSpo7Y+SSAbZ_eA9K6TqymvZ77YZ1kh9nstTDaW258wYUJ-Q@mail.gmail.com>
Date:	Mon, 12 Nov 2012 16:16:06 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	H Hartley Sweeten <hartleys@...ionengravers.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 Mon, Nov 12, 2012 at 4:13 PM, H Hartley Sweeten
<hartleys@...ionengravers.com> wrote:
> 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?

Yes, that's my understanding.
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