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

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Date:   Tue, 14 Jun 2022 20:09:12 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Steven Rostedt <rostedt@...dmis.org>, Arnd Bergmann <arnd@...db.de>
CC:     <catalin.marinas@....com>, <gregkh@...uxfoundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <suzuki.poulose@....com>, <maz@...nel.org>,
        <quic_psodagud@...cinc.com>, <quic_tsoni@...cinc.com>,
        <will@...nel.org>
Subject: Re: [PATCHv15 5/9] lib: Add register read/write tracing support

On 6/14/2022 8:02 PM, Steven Rostedt wrote:
> On Wed, 18 May 2022 22:14:14 +0530
> Sai Prakash Ranjan <quic_saipraka@...cinc.com> 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>
>> ---
>  From a tracing point of view, I do not see anything wrong with this patch.
>
> Acked-by: Steven Rostedt (Google) <rostedt@...dmis.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