linux-kernel - Re: [PATCH] tracing: Add register read and write tracing support

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Date:   Mon, 28 Sep 2020 07:17:48 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Prasad Sodagudi <psodagud@...eaurora.org>
Cc:     rostedt@...dmis.org, mingo@...hat.com, keescook@...omium.org,
        saiprakash.ranjan@...eaurora.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, anton@...msg.org, arnd@...db.de,
        catalin.marinas@....com, ccross@...roid.com, jbaron@...mai.com,
        jim.cromie@...il.com, joe@...ches.com, joel@...lfernandes.org
Subject: Re: [PATCH] tracing: Add register read and write tracing support

On Sun, Sep 27, 2020 at 05:34:50PM -0700, Prasad Sodagudi wrote:
> Add register read/write operations tracing support.
> ftrace events helps trace register read and write
> location details of memory mapped IO registers. Also
> add _no_log variants the writel_relaxed/readl_relaed
> APIs to avoid excessive logging for certain register
> operations.
> 
> Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
> ---
>  arch/arm64/include/asm/io.h    | 117 ++++++++++++++++++++++++++++++++++++++---
>  include/linux/iorw.h           |  20 +++++++
>  include/trace/events/rwio.h    |  51 ++++++++++++++++++
>  kernel/trace/Kconfig           |  11 ++++
>  kernel/trace/Makefile          |   1 +
>  kernel/trace/trace_readwrite.c |  30 +++++++++++
>  6 files changed, 222 insertions(+), 8 deletions(-)
>  create mode 100644 include/linux/iorw.h
>  create mode 100644 include/trace/events/rwio.h
>  create mode 100644 kernel/trace/trace_readwrite.c
> 
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index ff50dd7..db5acff 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -9,6 +9,7 @@
>  #define __ASM_IO_H
>  
>  #include <linux/types.h>
> +#include <linux/iorw.h>
>  #include <linux/pgtable.h>
>  
>  #include <asm/byteorder.h>
> @@ -24,24 +25,28 @@
>  #define __raw_writeb __raw_writeb
>  static inline void __raw_writeb(u8 val, volatile void __iomem *addr)
>  {
> +	log_write_io(addr);
>  	asm volatile("strb %w0, [%1]" : : "rZ" (val), "r" (addr));

You are just logging the address, what about the data written or read?
Why throw away half of the information here?

Oh, and sending patches that break the build is generally not a good
thing to do :)

thanks,

greg k-h