Re: [PATCH RFC 01/14] x86/asm: add iosubmit_cmds512() based on movdir64b CPU instruction

From: Thomas Gleixner
Date: Wed Nov 20 2019 - 19:53:16 EST

On Wed, 20 Nov 2019, Dan Williams wrote:
> On Wed, Nov 20, 2019 at 3:27 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
> >
> > On Wed, Nov 20, 2019 at 03:19:23PM -0800, Luck, Tony wrote:
> > > That's the underlying functionality of the MOVDIR64B instruction. A
> > > posted write so no way to know if it succeeded.
> >
> > So how do you know whether any of the writes went through?
> It's identical to the writel() mmio-write to start a SATA command
> transfer. The higher level device driver protocol validates that the
> command went through, ultimately with a timeout. There's no return
> value for iosubmit_cmds512() for the same reason there's no return
> value for the other iowrite primitives.

With the difference that other iowrite primitive have no dependencies on
cpu feature bits and cannot fail on the software level.