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

[Sai Prakash Ranjan]

Hi Arnd,

On 11/18/2021 8:54 PM, Arnd Bergmann wrote:
> On Mon, Nov 15, 2021 at 12:33 PM Sai Prakash Ranjan
> <quic_saipraka@xxxxxxxxxxx> wrote:
> >   /*
> >    * Generic IO read/write.  These perform native-endian accesses.
> >    */
> > -#define __raw_writeb __raw_writeb
> > -static inline void __raw_writeb(u8 val, volatile void __iomem *addr)
> > +static inline void arch_raw_writeb(u8 val, volatile void __iomem *addr)
> >   {
> >          asm volatile("strb %w0, [%1]" : : "rZ" (val), "r" (addr));
> >   }
> Woundn't removing the #define here will break the logic in
> include/asm-generic/io.h,
> making it fall back to the pointer-dereference version for the actual access?

#defines for these are added in mmio-instrumented.h header which is 
included in
arm64/asm/io.h, so it won't break the logic by falling back to 
pointer-dereference.

> > +#if IS_ENABLED(CONFIG_TRACE_MMIO_ACCESS) && !(defined(__DISABLE_TRACE_MMIO__))
> > +DECLARE_TRACEPOINT(rwmmio_write);
> > +DECLARE_TRACEPOINT(rwmmio_read);
> > +
> > +void log_write_mmio(const char *width, volatile void __iomem *addr);
> > +void log_read_mmio(const char *width, const volatile void __iomem *addr);
> > +
> > +#define __raw_write(v, a, _l)  ({                              \
> > +       volatile void __iomem *_a = (a);                        \
> > +       if (tracepoint_enabled(rwmmio_write))                   \
> > +               log_write_mmio(__stringify(write##_l), _a);     \
> > +       arch_raw_write##_l((v), _a);                            \
> > +       })
> This feels like it's getting too big to be inlined. Have you considered
> integrating this with the lib/logic_iomem.c infrastructure instead?
>
> That already provides a way to override MMIO areas, and it lets you do
> the logging from a single place rather than having it duplicated in every
> single caller. It also provides a way of filtering it based on the ioremap()
> call.

Thanks for the suggestion, will look at the logic_iomem.c and see if it 
fits our
usecase.

Thanks,
Sai