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

From: Dan Williams
Date: Wed Nov 20 2019 - 19:27:58 EST

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.