linux-kernel - Re: [PATCHv5 3/4] tracing: Add register read/write tracing support

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Date:   Mon, 6 Dec 2021 09:59:24 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Marc Zyngier <maz@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        quic_psodagud@...cinc.com,
        Prasad Sodagudi <psodagud@...eaurora.org>
Subject: Re: [PATCHv5 3/4] tracing: Add register read/write tracing support

On Mon, Dec 6, 2021 at 9:28 AM Sai Prakash Ranjan
<quic_saipraka@...cinc.com> wrote:
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 420ff4bc67fd..9f55bcc51de1 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -95,6 +95,13 @@ config RING_BUFFER_ALLOW_SWAP
>          Allow the use of ring_buffer_swap_cpu.
>          Adds a very slight overhead to tracing when enabled.
>
> +config TRACE_MMIO_ACCESS
> +       bool "Register read/write tracing"
> +       depends on TRACING
> +       help
> +         Create tracepoints for MMIO read/write operations. These trace events
> +         can be used for logging all MMIO read/write operations.

I think this needs a 'depends on ARCH_HAVE_TRACE_MMIO_ACCESS'
or similar.

> +void log_read_mmio(u8 width, const volatile void __iomem *addr)
> +{
> +       trace_rwmmio_read(CALLER_ADDR0, CALLER_ADDR1, width, addr);
> +}

Here, it may be better to pass the caller address as an argument, I think
CALLER_ADDR1 is not always reliable, though it's possible that it is
in the configurations when this file gets enabled.

       Arnd