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

Hi Arnd,

On 11/18/2021 8:54 PM, Arnd Bergmann wrote:

On Mon, Nov 15, 2021 at 12:33 PM Sai Prakash Ranjan
[off-list ref] wrote:

quoted

  /*
   * 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.

quoted

+#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



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