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Date:   Tue, 14 Jun 2022 10:32:05 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Sai Prakash Ranjan <quic_saipraka@quicinc.com>
Cc:     <arnd@arndb.de>, <catalin.marinas@arm.com>,
        <gregkh@linuxfoundation.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <coresight@lists.linaro.org>, <suzuki.poulose@arm.com>,
        <maz@kernel.org>, <quic_psodagud@quicinc.com>,
        <quic_tsoni@quicinc.com>, <will@kernel.org>,
        Prasad Sodagudi <psodagud@codeaurora.org>
Subject: Re: [PATCHv15 5/9] lib: Add register read/write tracing support
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On Wed, 18 May 2022 22:14:14 +0530
Sai Prakash Ranjan <quic_saipraka@quicinc.com> wrote:

> From: Prasad Sodagudi <psodagud@codeaurora.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@codeaurora.org>
> Co-developed-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
> ---

From a tracing point of view, I do not see anything wrong with this patch.

Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve