linux-kernel - Re: [PATCHv15 5/9] lib: Add register read/write tracing support

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Date:   Tue, 24 May 2022 09:29:38 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     <arnd@...db.de>, <rostedt@...dmis.org>
CC:     <gregkh@...uxfoundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <coresight@...ts.linaro.org>, <suzuki.poulose@....com>,
        <maz@...nel.org>, <quic_psodagud@...cinc.com>,
        <quic_tsoni@...cinc.com>, <will@...nel.org>,
        <catalin.marinas@....com>
Subject: Re: [PATCHv15 5/9] lib: Add register read/write tracing support

Hi Steve,

On 5/18/2022 10:14 PM, Sai Prakash Ranjan wrote:
> From: Prasad Sodagudi <psodagud@...eaurora.org>
>
> Generic MMIO read/write i.e., __raw_{read,write}{b,l,w,q} accessors
> are typically used to read/write from/to memory mapped registers
> and can cause hangs or some undefined behaviour in following few
> cases,
>
> * If the access to the register space is unclocked, for example: if
>    there is an access to multimedia(MM) block registers without MM
>    clocks.
>
> * If the register space is protected and not set to be accessible from
>    non-secure world, for example: only EL3 (EL: Exception level) access
>    is allowed and any EL2/EL1 access is forbidden.
>
> * If xPU(memory/register protection units) is controlling access to
>    certain memory/register space for specific clients.
>
> and more...
>
> Such cases usually results in instant reboot/SErrors/NOC or interconnect
> hangs and tracing these register accesses can be very helpful to debug
> such issues during initial development stages and also in later stages.
>
> So use ftrace trace events to log such MMIO register accesses which
> provides rich feature set such as early enablement of trace events,
> filtering capability, dumping ftrace logs on console and many more.
>
> Sample output:
>
> rwmmio_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
> rwmmio_post_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
> rwmmio_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 addr=0xfffffbfffdbff610
> rwmmio_post_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 val=0x0 addr=0xfffffbfffdbff610
>
> Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
> Co-developed-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>
> ---
>   arch/Kconfig                  |  3 ++
>   arch/arm64/Kconfig            |  1 +
>   include/trace/events/rwmmio.h | 97 +++++++++++++++++++++++++++++++++++
>   lib/Kconfig                   |  7 +++
>   lib/Makefile                  |  2 +
>   lib/trace_readwrite.c         | 47 +++++++++++++++++
>   6 files changed, 157 insertions(+)
>   create mode 100644 include/trace/events/rwmmio.h
>   create mode 100644 lib/trace_readwrite.c

How does this version look?

Thanks,
Sai