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SubjectRe: [PATCH v6 01/17] powerpc/vas: Define macros, register fields and structures
Nicholas Piggin [npiggin@gmail.com] wrote:
> On Mon, 14 Aug 2017 15:21:48 +1000
> Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> > Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
>
> > > arch/powerpc/include/asm/vas.h | 35 ++++
> > > arch/powerpc/include/uapi/asm/vas.h | 25 +++
> >
> > I thought we weren't exposing VAS to userspace yet?
> >
> > If we are then we need to get things straight WRT copy/paste abort.
>

> No we should not be. This might be just a leftover hunk that should
> be moved to a future series.

Yes, I should have posted patches 14..17 separately as an RFC that goes
on top of the VAS kernel patches 1..13.

>
> At the moment (as far as I understand) it should be limited to
> preempt-disabled, process context, kernel users which avoids any
> concern for switch_to.
>

In the FTW case, there is no data transfer from user space to the hardware.
i.e the copy/paste submit a NULL CRB and hardware will be configured (see
->fifo_disable setting in winctx) to ignore any data they specify in the CRB.

Would we be able to allow copy/paste from user space in that case?

Sukadev

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