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

[Sai Prakash Ranjan]

On 11/22/2021 9:05 PM, Arnd Bergmann wrote:
> On Mon, Nov 22, 2021 at 3:59 PM Sai Prakash Ranjan
> <quic_saipraka@xxxxxxxxxxx> wrote:
> > > > 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. Arnd
> > Sorry, I didn't get this part, so  I am trying this on ARM64:
> >
> > arm64/include/asm/io.h has read{b,l,w,q} defined.
> > include/asm-generic/io.h has below:
> >     #ifndef readl
> >     #define readl readl
> >     static inline u32 readl(const volatile void __iomem *addr)
> >
> > and we include asm-generic/io.h in arm64/include/asm/io.h at the end
> > after the definitions for arm64 mmio accesors.
> > So arch implementation here overrides generic ones as I see it, am I
> > missing something? I even confirmed this
> > with some trace_printk to generic and arch specific definitions of readl
> > and I see arch specific ones being called.
> Ah, you are right that the arm64 version currently has custom definitions
> of the high-level interfaces. These predate the introduction of the
> __io_{p,}{b,a}{r,w} macros and are currently only used on risc-v.
>
> I think in this case you should start by changing arm64 to use the
> generic readl() etc definitions, by removing the extra definitions and
> using
>
> #define __io_ar(v) __iormb(__v)
> #define __io_bw() dma_wmb()

Sure, will do that.

Thanks,
Sai