Re: [PATCH v4 1/5] io: define several IO & PIO barrier types for the asm-generic version

[okaya]

On 2018-04-06 06:19, Arnd Bergmann wrote:
> On Thu, Apr 5, 2018 at 3:09 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> 
> wrote:
> > Getting ready to harden readX()/writeX() and inX()/outX() semantics 
> > for the
> > generic implementation.
> >
> > Defining two set of macros as __io_br() and __io_ar() to indicate 
> > actions
> > to be taken before and after MMIO read.
> >
> > Defining two set of macros as __io_bw() and __io_aw() to indicate 
> > actions
> > to be taken before and after MMIO write.
> >
> > Defining two set of macros as __io_pbw() and __io_paw() to indicate 
> > actions
> > to be taken before and after Port IO write.
> >
> > Defining two set of macros as __io_pbr() and __io_par() to indicate 
> > actions
> > to be taken before and after Port IO read.
> >
> > If rmb() is available for the architecture, prefer rmb() as the 
> > default
> > implementation of __io_ar()/__io_par().
> >
> > If wmb() is available for the architecture, prefer wmb() as the 
> > default
> > implementation of __io_bw()/__io_pbw().
> >
> > Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
>
> I've applied the series to my asm-generic tree now, I will give it a 
> few days
> in linux-next to see if any obvious regressions happen, and then send
> a pull request.
>
> Checking the list of architectures that are affected by this, I see
> h8300, microblaze, nios2, openrisc, s390, sparc, um, unicore32,
> and xtensa, all of which use asm-generic/io.h without overriding
> the default readl/writel.
>
> I would guess that at least s390 doesn't need the barriers
> (maintainers on Cc now), but there may be others that want to
> override the new barriers with weaker ones where an MMIO
> access is guaranteed to serialize against DMA, or where
> a specialized barrier for this case exists.
>
> Looking over the asm-generic implementation once more now,
> I wonder if we should change the relaxed accessors to not have
> any barriers (back to the version before your series) rather than
> defaulting them to having the same barriers as the regular
> readl/writel.

I can do a follow up patch. You want to map them to raw api without any 
barriers as before. Right?


>      Arnd