Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to __io_par()

From: Will Deacon
Date: Wed Feb 13 2019 - 12:46:21 EST

On Tue, Feb 12, 2019 at 12:55:17PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 11, 2019 at 6:45 PM Will Deacon <will.deacon@xxxxxxx> wrote:
> >
> > The inX() I/O accessors must enforce ordering against subsequent calls
> > to the delay() routines, so that a read-back from a device can be used
> > to postpone a subsequent write to the same device.
> >
> > On some architectures, including arm64, this ordering can only be
> > achieved by creating a dependency on the value returned by the inX()
> > operation, so we need to pass the value we read to the __io_par()
> > macro in this case.
> >
> > Reported-by: Andrew Murray <andrew.murray@xxxxxxx>
> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> > ---
> > include/asm-generic/io.h | 8 ++++----
> For changing the asm-generic file in the arm64 tree,
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

Thanks, Arnd.

> For all I can see, this should not conflict with the usage of the
> same macros on RISC-V, though it does make add a significant
> difference, so I'd like to see an Ack from the RISC-V folks as
> well (added to Cc), or possibly a change to arch/riscv/include/asm/io.h
> to do a corresponding change.

There's already a comment in that header which says that the accesses are
ordered wrt timer reads, so I don't think anything needs to change there.
For consistency with the macro arguments, I could augment their __io_par to
take the read value as an unused argument, if that's what you mean?