Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

From: Arnd Bergmann
Date: Mon Nov 22 2021 - 09:30:52 EST

On Mon, Nov 22, 2021 at 3:19 PM Sai Prakash Ranjan
<quic_saipraka@xxxxxxxxxxx> wrote:
> On 11/22/2021 7:29 PM, Arnd Bergmann wrote:
> >
> > I think this would be a lot less confusing to readers, as it is implemented
> > exactly in the place that has the normal definition, and it can also have
> > somewhat more logical semantics by only instrumenting the
> > normal/relaxed/ioport accessors but not the __raw_* versions that
> > are meant to be little more than a pointer dereference.
> But how is this different from logic in atomic-instrumented.h which also
> has asm-generic version?
> Initial review few years back mentioned about having something similar
> to atomic instrumentation
> and hence it was implemented with the similar approach keeping
> instrumentation out of arch specific details.

This is only a cosmetic difference. I usually prefer fewer indirections,
and I like the way that include/asm-generic/io.h only has all the
normal 'static inline' definitions spelled out, and calling the __raw_*
versions. Your version adds an extra layer with the arch_raw_readl(),
which I'd prefer to avoid.

> And if we do move this instrumentation to asm-generic/io.h, how will
> that be executed since
> the arch specifc read{b,w,l,q} overrides this generic version?

As I understand it, your version also requires architecture specific
changes, so that would be the same: it only works for architectures
that get the definition of readl()/readl_relaxed()/inl()/... from
include/asm-generic/io.h and only override the __raw version.