Re: [PATCHv5 4/4] asm-generic/io: Add logging support for MMIO accessors
From: Arnd Bergmann <arnd@arndb.de>
Date: 2021-12-06 09:10:16
Also in:
linux-arm-msm, lkml
On Mon, Dec 6, 2021 at 9:28 AM Sai Prakash Ranjan [off-list ref] wrote:
quoted hunk ↗ jump to hunk
+#if IS_ENABLED(CONFIG_TRACE_MMIO_ACCESS) && !(defined(__DISABLE_TRACE_MMIO__)) +#include <linux/tracepoint-defs.h> + +DECLARE_TRACEPOINT(rwmmio_write); +DECLARE_TRACEPOINT(rwmmio_read); + +#define rwmmio_tracepoint_active(t) tracepoint_enabled(t) +void log_write_mmio(u64 val, u8 width, volatile void __iomem *addr); +void log_read_mmio(u8 width, const volatile void __iomem *addr); + +#else + +#define rwmmio_tracepoint_active(t) false +static inline void log_write_mmio(u64 val, u8 width, volatile void __iomem *addr) {} +static inline void log_read_mmio(u8 width, const volatile void __iomem *addr) {} + +#endif /* CONFIG_TRACE_MMIO_ACCESS */ /* * __raw_{read,write}{b,w,l,q}() access memory in native endianness.@@ -149,6 +166,8 @@ static inline u8 readb(const volatile void __iomem *addr) { u8 val; + if (rwmmio_tracepoint_active(rwmmio_read)) + log_read_mmio(8, addr); __io_br(); val = __raw_readb(addr); __io_ar(val);
For readability, it may be nicer to fold the two lines you add for each
helper into one, such as
void __log_write_mmio(u64 val, u8 width, volatile void __iomem *addr);
#define log_write_mmio(val, widtg, addr) do { \
if (tracepoint_enabled(rwmmio_read)) \
__log_write_mmio((val), (width), (addr)); \
} while (0)
I wonder if it may even be better to not check for tracepoint_active() in the
inline function at all but always enter the external function when built-in.
This means we do run into the branch, but it also reduces the i-cache footprint.
For general functionality, I think it would be better to trace the returned
value from the read, but I don't know if that defeats the purpose you
are interested in, since it requires the tracing to come after the __raw_read.
Arnd
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