Re: [PATCH] add delay between port write and port read

From: Arnd Bergmann (arnd@xxxxxxxx)
Date: Tue Feb 19 2019 - 09:30:57 EST

On Tue, Feb 19, 2019 at 2:44 PM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> On Tue, 19 Feb 2019, Mikulas Patocka wrote:
> > The patches cd0e00c106722eca40b38ebf11cf134c01901086 and
> > 92d7223a74235054f2aa7227d207d9c57f84dca0 fix a theoretical issue where the
> > code didn't follow the specification. Unfortunatelly, they also reduce
> > timing when port write is followed by a port read.
> >
> > These reduced timing cause hang on boot on the Avanti platform when
> > probing serial ports. This patch adds memory barrier after the outb, outw,
> > outl functions, so that there is delay between port write and subsequent
> > port read - just like before.
> >
> > Fixes: cd0e00c10672 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering")
> > Cc: stable@xxxxxxxxxxxxxxx # v4.17+
> you can also add:
> Tested-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

but I notice you are missing Signed-off-by.

We clearly need this patch, but I assumed the alpha maintainers would pick
it up, not me. I merged the original changes since they were cross-architecture,
but I don't normally take patches for a particular architecture through the
asm-generic tree (or the soc tree for that matter).