linux-kernel - Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

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Message-ID: <b07e339c-530d-683c-c626-14b73b42e72a@quicinc.com>
Date:   Fri, 19 Nov 2021 09:36:39 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Catalin Marinas <catalin.marinas@....com>,
        <quic_psodagud@...cinc.com>, "Marc Zyngier" <maz@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access
 instrumentation

Hi Arnd,

On 11/18/2021 8:54 PM, Arnd Bergmann wrote:
> On Mon, Nov 15, 2021 at 12:33 PM Sai Prakash Ranjan
> <quic_saipraka@...cinc.com> wrote:
>>   /*
>>    * Generic IO read/write.  These perform native-endian accesses.
>>    */
>> -#define __raw_writeb __raw_writeb
>> -static inline void __raw_writeb(u8 val, volatile void __iomem *addr)
>> +static inline void arch_raw_writeb(u8 val, volatile void __iomem *addr)
>>   {
>>          asm volatile("strb %w0, [%1]" : : "rZ" (val), "r" (addr));
>>   }
> Woundn't removing the #define here will break the logic in
> include/asm-generic/io.h,
> making it fall back to the pointer-dereference version for the actual access?

#defines for these are added in mmio-instrumented.h header which is 
included in
arm64/asm/io.h, so it won't break the logic by falling back to 
pointer-dereference.

>> +#if IS_ENABLED(CONFIG_TRACE_MMIO_ACCESS) && !(defined(__DISABLE_TRACE_MMIO__))
>> +DECLARE_TRACEPOINT(rwmmio_write);
>> +DECLARE_TRACEPOINT(rwmmio_read);
>> +
>> +void log_write_mmio(const char *width, volatile void __iomem *addr);
>> +void log_read_mmio(const char *width, const volatile void __iomem *addr);
>> +
>> +#define __raw_write(v, a, _l)  ({                              \
>> +       volatile void __iomem *_a = (a);                        \
>> +       if (tracepoint_enabled(rwmmio_write))                   \
>> +               log_write_mmio(__stringify(write##_l), _a);     \
>> +       arch_raw_write##_l((v), _a);                            \
>> +       })
> This feels like it's getting too big to be inlined. Have you considered
> integrating this with the lib/logic_iomem.c infrastructure instead?
>
> That already provides a way to override MMIO areas, and it lets you do
> the logging from a single place rather than having it duplicated in every
> single caller. It also provides a way of filtering it based on the ioremap()
> call.
>

Thanks for the suggestion, will look at the logic_iomem.c and see if it 
fits our
usecase.

Thanks,
Sai