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Message-ID: <e9472213-7127-9265-88d2-6f58a97c76d2@quicinc.com>
Date:   Tue, 14 Jun 2022 20:09:12 +0530
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Subject: Re: [PATCHv15 5/9] lib: Add register read/write tracing support
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To:     Steven Rostedt <rostedt@goodmis.org>, Arnd Bergmann <arnd@arndb.de>
CC:     <catalin.marinas@arm.com>, <gregkh@linuxfoundation.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <suzuki.poulose@arm.com>, <maz@kernel.org>,
        <quic_psodagud@quicinc.com>, <quic_tsoni@quicinc.com>,
        <will@kernel.org>
References: <cover.1652891705.git.quic_saipraka@quicinc.com>
 <f6d1b9e9d70968b506bdfd1b77129cb751b9df9d.1652891705.git.quic_saipraka@quicinc.com>
 <20220614103205.2d134546@gandalf.local.home>
From:   Sai Prakash Ranjan <quic_saipraka@quicinc.com>
In-Reply-To: <20220614103205.2d134546@gandalf.local.home>
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On 6/14/2022 8:02 PM, Steven Rostedt wrote:
> 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

Thanks Steve.

Hi Arnd, I hope we can take this series in your tree or let me know if anything else is pending?

Thanks,
Sai