Re: Q: Kconfig option VIRT_TO_BUS

Bjorn Helgaas
2012-11-12T23:16:29Z

On Mon, Nov 12, 2012 at 4:13 PM, H Hartley Sweeten
<hartleys@visionengravers.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.